ECE - Electronic Devices and Circuits Quiz (or) MCQ

1 .

What type of semiconductor is used in LED electronic circuits?

A)

Intrinsic semiconductor

B)

Degenerated semiconductor

C)

Compound semiconductor

D)

Compensated semiconductor

Correct Answer : Compound semiconductor

Explanation : LEDs need compound type semiconductors because they have direct band gap. In direct band gap, photons are easily generated when electrons release energy during recombination.

2 .

Which of the following semiconductor is mostly used to construct electronic circuits?

A)

Tin

B)

Silicon

C)

Selenium

D)

Germanium

Correct Answer : Silicon

Explanation : Silicon is mostly used to construct electronic circuits because silicon has a much higher PIV (Peak Inverse Voltage) than the other semiconductors. It is also very cheap.

3 .

At room temperature the current in an intrinsic semiconductor is due to

A)

ions

B)

holes

C)

electrons

D)

holes and electrons

Correct Answer : holes and electrons

Explanation : Intrinsic material has equal number of holes and electrons.

4 .

The most commonly used semiconductor material is

A)

silicon

B)

germanium

C)

mixture of silicon and germanium

D)

None of the above

Correct Answer : silicon

Explanation : Germanium is rarely used.

5 .

In which of these is reverse recovery time nearly zero?

A)

PIN diode

B)

Tunnel diode

C)

Zener diode

D)

Schottky diode

Correct Answer : Schottky diode

Explanation : In schottky diode there is no charge storage and hence almost zero reverse recovery time.

6 .

A transistor has a current gain of 0.99 in the CB mode. Its current gain in the CC mode is

A)

100

B)

99

C)

1.01

D)

0.99

Correct Answer : 100

Explanation :

7 .

Which of the following is not an electronic device?

A)

A mobile

B)

A keyboard

C)

A magnifying glass

D)

A computer

Correct Answer : A magnifying glass

Explanation : A mobile, a computer and a keyboard are electronics devices because they are controlled by the flow of electrons for information processing. A magnifying glass is a non-electronic device.

8 .

Which of the following is not a physical component of an electronic circuit?

A)

Diode

B)

Temperature

C)

Inductor

D)

Capacitor

Correct Answer : Temperature

Explanation : Capacitors, inductors, and diodes are the physical components of electronic circuits because they affect the flow of electrons or current in the circuit.

9 .

Which of the following is not a property of semiconductors used in electronic devices?

A)

They donâ€™t emit light

B)

They excite electrons

C)

They have high thermal conductivity

D)

They have variable electrical conductivity

Correct Answer : They donâ€™t emit light

Explanation : Semiconductors excite electrons. They have variable electrical conductivity and high thermal conductivity. Some compound semiconductors also emit light which is popularly known as light-emitting diodes.

10 .

What is the effect of temperature on the recombination rate of electrons in electronic circuits?

A)

Recombination rate is independent of temperature

B)

Recombination of electrons doesnâ€™t occur in semiconductors

C)

Recombination rate increases with increase in the temperature

D)

Recombination rate decreases with increase in the temperature

Correct Answer : Recombination rate decreases with increase in the temperature

Explanation : Recombination rate decreases when temperature increases because the electrons that are going to combine with holes in the valence bond are re-excited.

11 .

The amount of photoelectric emission current depends on

A)

frequency of incident radiation

B)

intensity of incident radiation

C)

both frequency and intensity of incident radiation

D)

None of the above

Correct Answer : intensity of incident radiation

Explanation : Only the intensity of incident radiation governs the amount of photoelectric emission.

12 .

At very high temperatures the extrinsic semi conductors become intrinsic because

A)

drive in diffusion of dopants and carriers

B)

band to band transition is balanced by impurity ionization

C)

band to band transition dominants over impurity ionization

D)

impurity ionization dominants over band to band transition

Correct Answer : band to band transition dominants over impurity ionization

Explanation : Covalent bonds are broken

13 .

In an n-p-n transistor, the majority carriers in the base are

A)

holes

B)

electrons

C)

both holes and electrons

D)

either holes or electrons

Correct Answer : electrons

Explanation : Emitter is n type and emits electrons which diffuse through the base.

14 .

When a voltage is applied to a semiconductor crystal then the free electrons will flow.

A)

towards negative terminal

B)

towards positive terminal

C)

either towards positive terminal or negative terminal

D)

towards positive terminal for 1 Î¼s and towards negative terminal for next 1 Î¼s

Correct Answer : towards positive terminal

Explanation : Since electrons are negatively charged they will flow towards positive terminal.

15 .

Ferrite have___________.

A)

low resistivity

B)

low copper loss

C)

low eddy current loss

D)

higher specific gravity compared to iron

Correct Answer : low resistivity

Explanation :

Ferrite is a low density material of composition with Fe₂O₃ x O, where x is a bivalent metal, such as Cobart, Ni, Mn. These magnetic materials having very low loss of current and used in high frequency circuit.

16 .

An LED has a rating of 2 V and 10 mA. It is used along with 6V battery. The range of series resistance is

A)

0 to 200 Î©

B)

200 - 400 Î©

C)

200 Î© and above

D)

400 Î© and above

Correct Answer : 400 Î© and above

Explanation :

17 .

The number of doped regions in PIN diode is

A)

1

B)

2

C)

3

D)

1 or 2

Correct Answer : 2

Explanation : A PIN diode has p and n doped regions separated by intrinsic layer.

18 .

A transistor has two p-n junctions. The batteries should be connected such that

A)

both junctions are forward biased

B)

both junctions are reverse biased

C)

one junction is forward biased and the other is reverse biased

D)

None of the above

Correct Answer : one junction is forward biased and the other is reverse biased

Explanation : Emitter-base junction is forward biased and base collector junction is reverse biased.

19 .

A silicon (PN) junction at a temperature of 20Â°C has a reverse saturation current of 10 pico Ampere. The reverse saturation current at 40Â°C for the same bias is approximately.

A)

30 pA

B)

40 pA

C)

50 pA

D)

60 pA

Correct Answer : 40 pA

Explanation :

By increasing of temperature by 10°C, I_o become double so by increasing temperature 20°C, I_o become 4 time than initial value... and it is 40 PA.

20 .

Which of the following is correct about semiconductors in electronic devices?

A)

Doping is done in Intrinsic semiconductors

B)

Elemental semiconductors have direct band gap

C)

Compound semiconductors have indirect band gap

D)

Extrinsic semiconductors are injected with impurities

Correct Answer : Extrinsic semiconductors are injected with impurities

Explanation : Elemental semiconductors have indirect band gap. Compound semiconductors have direct band gap. Doping is done with impurities in extrinsic semiconductors, not in intrinsic semiconductors.

21 .

Which of the following technique canâ€™t be used for generating electron-hole pairs in electronic devices?

A)

Impurity injection

B)

Photo excitation

C)

Impact ionization

D)

Thermal excitation

Correct Answer : Impurity injection

Explanation : Electron-hole pairs can be generated by increasing temperature or ionization or photo excitation. Impurity injection is done for doping of semiconductors. This process doesn’t generate electron-hole pairs.

22 .

Which of the following is not correct about semiconductors in electronic devices?

A)

Degenerated semiconductors behave like a conductor

B)

Electrons are present below Fermi level in a semiconductor

C)

Fermi level is independent of temperature and doping

D)

Pentavalent atoms are used in an n-type extrinsic semiconductor

Correct Answer : Fermi level is independent of temperature and doping

Explanation : Fermi level is the highest level of electrons at 0K. Below Fermi level, all levels are filled with electrons. Fermi level depends on the temperature and the doping of the semiconductor.

23 .

Which of the following is correct about Hall Effect in electronic circuits?

A)

Hall voltage is directly proportional to the charge density

B)

Hall voltage is very weak in metals as compared to semiconductors

C)

Hall voltage is inversely proportional to the intensity of the magnetic field

D)

Intrinsic semiconductor has a positive temperature coefficient of hall constant

Correct Answer : Hall voltage is very weak in metals as compared to semiconductors

Explanation : Metals have an ocean of electrons. So, there is very little difference between positive and negative charges in metals. Thus, Hall voltage is very weak in metals as compared to semiconductors.

24 .

Which of the following is not correct about a step-graded junction in electronic devices?

A)

They are designed with abrupt junction

B)

Diodes with step-graded junctions are slower than a normal diode

C)

Depletion layer penetrates more into the lightly doped region

D)

None of the above

Correct Answer : Diodes with step-graded junctions are slower than a normal diode

Explanation : Step-graded junctions are designed with abrupt junctions. They are either p⁺– n or p – n⁺ junction and diodes with step-graded junctions are faster than the normal diodes.

25 .

The forbidden energy gap between the valence band and conduction band will be least in case of

A)

Metals

B)

Insulators

C)

Semiconductors

D)

All of the above

Correct Answer : Metals

26 .

For a NPN bipolar transistor, what is the main stream of current in the base region?

A)

Drift of electrons

B)

Drift of holes

C)

Diffusion of electrons

D)

Diffusion of holes

Correct Answer : Diffusion of holes

27 .

For a P-N diode, the number of minority carriers crossing the junction depends on

A)

Potential barrier

B)

Forward bias voltage

C)

Rate of thermal generation of electron hole pairs

D)

None of the above

Correct Answer : Rate of thermal generation of electron hole pairs

28 .

An electron in the conduction band

A)

Loses its charge easily

B)

Jumps to the top of the crystal

C)

Has lower energy than the electron in the valence band

D)

Has higher energy than the electron in the valence band

Correct Answer : Has higher energy than the electron in the valence band

29 .

What is the necessary a.c. input power from the transformer secondary used in a half wave rectifier to deliver 500 W of d.c. power to the load?

A)

308 W

B)

616 W

C)

848 W

D)

1232 W

Correct Answer : 1232 W

30 .

A thermistor is a

A)

Thermometer

B)

Miniature resistance

C)

Thermocouple

D)

Heat sensitive explosive

Correct Answer : Miniature resistance

31 .

Each cell of a static Random Access memory contains

A)

6 MOS transistor

B)

4 MOS transistor, 2 capacitor

C)

2 MOS transistor, 4 capacitor

D)

1 MOS transistor and 1 capacitor

Correct Answer : 6 MOS transistor

32 .

The dynamic resistance of a forward biased p-n diode

A)

Is constant

B)

Varies directly with current

C)

Varies inversely with current

D)

Is either constant or varies directly with current

Correct Answer : Varies inversely with current

33 .

In an ideal diode there is no breakdown, no __________ current, and no forward __________ drop.

A)

Reverse, current

B)

Forward, voltage

C)

Reverse, voltage

D)

Forward, current

Correct Answer : Reverse, voltage

34 .

Which of the following is correct about photo diode electronic devices?

A)

It is a photovoltaic cell

B)

P-N junction is connected in reverse bias.

C)

Electron-hole pairs are generated by impurity injection in depletion layer

D)

No external voltage is applied

Correct Answer : P-N junction is connected in reverse bias.

Explanation : Photo diode is a photoconductive cell. External voltage is applied and P-N junction is connected in reverse bias. Electron-hole pairs are generated by photons in the depletion layer.

35 .

Which of the following is wrong about solar cell electronic devices?

A)

It produces dark current

B)

It is a photovoltaic cell

C)

No external voltage is applied

D)

Solar cell responsivity is directly proportional to the wavelength of light

Correct Answer : It produces dark current

Explanation : Solar cell is a photovoltaic cell. No external voltage is applied and solar cell responsivity is directly proportional to the wavelength of the incident light. It doesn’t produce dark current.

36 .

Which of the following is correct about NMOS electronic circuits?

A)

It has N-substrate

B)

NMOS has holes as the majority of carriers

C)

For accumulation positive voltage is applied to the gate terminal

D)

For inversion positive voltage is applied to the gate terminal

Correct Answer : For inversion positive voltage is applied to the gate terminal

Explanation : NMOS has P-substrate and it has electrons as the majority carriers. For accumulation negative voltage is applied to the gate terminal and for inversion positive voltage is applied to the gate terminal.

37 .

Which of the following is wrong about threshold voltage (V_T) in a MOSFET electronic circuit?

A)

V_T is independent of ion implementation

B)

If V_T is less, channel form quickly for conductivity

C)

V_T can be reduced by reducing substrate doping

D)

V_T can be reduced by reducing oxide layer thickness

Correct Answer : V_T is independent of ion implementation

Explaination : V_T can be reduced by suitable ion implementation. Like in NMOS, positive donor ions are implemented to reduce repulsion to the electrons present in the channel.

38 .

In which of the following region does BJT act as the amplifier electronic device?

A)

Active

B)

Cut-off

C)

Saturation

D)

Reverse saturation

Correct Answer : Reverse saturation

Explanation : In the active region, the emitter-base junction is forward biased, the collector-base junction is reversed biased. This is the operating mode when amplification of signals occurs in BJT.

39 .

Which type of semiconductor is used in Tunnel Diode?

A)

Extrinsic semiconductor

B)

Elemental semiconductor

C)

Degenerated semiconductor

D)

Compound semiconductor

Correct Answer : Degenerated semiconductor

Explanation : Degenerative N-type and degenerative p-type semiconductors are used in tunnel diodes. Tunnel diodes are used in microwave electronic devices and circuits.

40 .

As compared to an ordinary semiconductor diode, a Schottky diode

A)

has higher cut in voltage

B)

has lower cut in voltage

C)

lower reverse saturation current

D)

Both (A) and (C)

Correct Answer : has lower cut in voltage

Explanation : Cut in voltage in Schottky diode is about 0.3 V as compared to 0.7 V in ordinary semiconductor diode.

41 .

Assertion (A) : When a high reverse voltage is applied to a p-n junction the diode breaks down.

Reason (R) : High reverse voltage causes Avalanche effect.

A)

A is true but R is false

B)

A is false but R is true

C)

Both A and R are true and R is correct explanation of A

D)

Both A and R are true but R is not a correct explanation of A

Correct Answer : Both A and R are true and R is correct explanation of A

Explaination : Avalanche breakdown occurs at high reverse voltage.

42 .

Crossover distortion behaviour is characteristic of

A)

class B O/P stage

B)

class A O/P stage

C)

class AB output stage

D)

common pulse O/P state

Correct Answer : class B O/P stage

Explanation : It is a characteristics of class B output stage as the amplifier is biased in cut-off region.

In class B amplifier, two transistor are operated in such a way that one is amplify the half cycle and second is amplify -ve half cycle.

43 .

In an n-p-n transistor biased for operation in forward active region

A)

emitter is positive with respect to base

B)

collector is positive with respect to base

C)

base is positive with respect to emitter and collector is positive with respect to base

D)

None of the above

Correct Answer : base is positive with respect to emitter and collector is positive with respect to base

Explanation : In forward active mode emitter base junction is forward biased and base collector junction is reverse biased.

44 .

A zener diode is used in

A)

amplifier circuits

B)

voltage regulator circuit

C)

both voltage regulator and amplifier circuit

D)

None of the above

Correct Answer : voltage regulator circuit

Explanation : Zener diode is used only in voltage regulator circuits.

45 .

In a zener diode

A)

there are two p-n junctions

B)

the ratio v-i can be negative

C)

the forward current is very high

D)

sharp breakdown occurs at a certain reverse voltage

Correct Answer : sharp breakdown occurs at a certain reverse voltage

Explanation : When reverse voltage equals breakdown value it starts conducting and voltage does not increase further.

46 .

In a bipolar transistor which current is largest

A)

emitter current

B)

base current

C)

collector current

D)

base current or emitter current

Correct Answer : emitter current

Explanation : Emitter current is larger, collector current is slightly less than emitter current and base current is very small.

47 .

In a degenerate n type semiconductor material, the Fermi level,

A)

is in valence band

B)

is in conduction band

C)

is very near valence band

D)

is at the centre in between valence and conduction bands

Correct Answer : is in conduction band

Explanation : This is due to high level of doping.

48 .

The types of carriers in a semiconductor are

A)

1

B)

2

C)

3

D)

4

Correct Answer : 2

Explanation : Holes and electrons.

49 .

A potential of 7 V is applied to a silicon diode. A resistance of 1 K ohm is also in series with the diode. The current is

A)

0

B)

0.7 mA

C)

6.3 mA

D)

7 mA

Correct Answer : 6.3 mA

Explanation :

50 .

Calculate the stability factor and change in I_C from 25°C to 100°C for, β = 50, R_B/ R_E = 250, ΔI_C0 = 19.9 nA for emitter bias configuration.

A)

40.91, 0.58 μA

B)

40.91, 0.58 μA

C)

41.10, 0.39 μA

D)

42.53, 0.85 μA

Correct Answer : 42.53, 0.85 μA

Explaination :

51 .

The word enhancement mode is associated with

A)

JFET

B)

MOSFET

C)

tunnel diode

D)

photo diode

Correct Answer : MOSFET

Explanation : MOSFET may be depletion mode or enhancement mode.

52 .

In which region of a CE bipolar transistor is collector current almost constant?

A)

Active region

B)

Saturation region

C)

Breakdown region

D)

Both saturation and active region

Correct Answer : Active region

Explanation : It is used as amplifier when it operates in this region.

53 .

A p-n junction diode has

A)

a non-linear v-i characteristics

B)

low forward and high reverse resistance

C)

zero forward current till the forward voltage reaches cut in value

D)

All of the above

Correct Answer : All of the above

Explanation : A p-n Junction has all these features.

54 .

Which of the following is true as regards photo emission?

A)

Velocity of emitted electrons is dependent on light intensity

B)

Rate of photo emission is inversely proportional to light intensity

C)

Maximum velocity of electron increases with decreasing wave length

D)

Both holes and electrons are produced

Correct Answer : Maximum velocity of electron increases with decreasing wave length

Explanation : As wavelength decreases, frequency increases and maximum velocity of electron increases.

55 .

The normal operation of JFET is

A)

constant voltage region

B)

constant current region

C)

either constant voltage or constant current region

D)

both constant voltage and constant current regions

Correct Answer : constant current region

Explanation : In major portion of drain characteristics ID is constant.

56 .

The power dissipation in a transistor is the product of

A)

emitter current and emitter to base voltage

B)

emitter current and collector to emitter voltage

C)

collector current and collector to emitter voltage

D)

None of the above

Correct Answer : collector current and collector to emitter voltage

Explanation : Maximum power dissipation occurs at collector junction.

57 .

An incremental model of a solid state device is one which represents the

A)

ac property of the device at desired operating point

B)

dc property of the device at all operating points

C)

ac property of the device at all operating points

D)

complete ac and dc behaviour at all operating points

Correct Answer : ac property of the device at desired operating point

Explanation : Incremental model is used for ac response at one operating point.

58 .

Which of the following is used for generating time varying wave forms?

A)

UJT

B)

MOSFET

C)

PIN diode

D)

Tunnel diode

Correct Answer : UJT

Explanation : Its output is used to trigger SCR.

59 .

Calculate the resistivity of n-type semiconductor from the following data, Density of holes = 5 x 10¹² cm^-3. Density of electrons = 8 x 10¹³ cm^-3, mobility of conduction electron = 2.3 x 10⁴ cm²/ V-sec and mobility of holes = 100 cm²/V-sec.

A)

0.24 Ω-m

B)

0.34 Ω-m

C)

0.42 Ω-m

D)

0.43 Ω-m

Correct Answer : 0.34 Ω-m

Explaination :

60 .

n-type semiconductors

A)

are negatively charged

B)

are produced when indium is added as impurity to germanium

C)

are produced when phosphorus is added as impurity to silicon

D)

None of the above

Correct Answer : are produced when phosphorus is added as impurity to silicon

Explanation : n type semiconductor is produced when pentavalent impurity is added.

61 .

The voltage across a zener diode

A)

is constant in forward direction

B)

is constant in reverse direction

C)

is constant in both forward and reverse directions

D)

None of the above

Correct Answer : is constant in reverse direction

62 .

In all metals_________

A)

current flow by electrons as well as by holes

B)

resistivity decreases with increase in temperature

C)

conductivity decreases with increase in temperature

D)

the gap between valence and conduction bands is small

Correct Answer : conductivity decreases with increase in temperature

Explanation : In all metals conductivity decreases (and resistance increases) with increase in temperature.

63 .

The threshold voltage of an n-channel enhancement mode MOSFET is 0.5 when the device is biased at a gate voltage of 3V. Pinch off would occur at a drain voltage of

A)

1.5 V

B)

2.5 V

C)

3.5 V

D)

4.5 V

Correct Answer : 2.5 V

Explaination : It is used with reverse bias.

64 .

Which of these has degenerate p and n materials?

A)

PIN diode

B)

Zener diode

C)

Photo diode

D)

Tunnel diode

Correct Answer : Tunnel diode

Explanation : Tunnel diode has heavily doped p and n layers called degenerate p and n materials.

65 .

A Schottky diode clamp is used along with switching BJT for

A)

reducing the switching time

B)

increasing the value of Î²

C)

reducing the base current

D)

reducing the power dissipation

Correct Answer : reducing the switching time

Explanation : Schottky diode has very low switching time.

66 .

In a piezoelectric crystal, applications of a mechanical stress would produce

A)

shift in the Fermi level

B)

electrical polarization in the crystal

C)

magnetic dipoles in the crystal

D)

plastic deformation of the crystal

Correct Answer : electrical polarization in the crystal

Explanation : In piezoelectric materials mechanical stress produces electric polarization.

67 .

In which of the following is the width of junction barrier very small?

A)

Schottky diode

B)

PIN diode

C)

Photo diode

D)

Tunnel diode

Correct Answer : Schottky diode

Explanation : Schottky diode has very small depletion layer.

68 .

If the reverse voltage across a p-n junction is increased three times, the junction capacitance

A)

will increase

B)

will decrease

C)

will decrease by an approximate factor of about 2

D)

will increase by an approximate factor of about 2

Correct Answer : will decrease by an approximate factor of about 2

Explanation : Increase of reverse voltage widens the depletion layer and junction capacitance decreases. However the decrease in capacitance is not proportional to increase in voltage.

69 .

The units for transconductance are

A)

volts

B)

siemens

C)

ohms

D)

amperes

Correct Answer : siemens

Explanation : Its units are the same as the units of conductance.

70 .

Measurement of Hall coefficient enables the determination of

A)

recovery time of stored carrier

B)

Fermi level and forbidden energy gap

C)

temperature coefficient and thermal conductivity

D)

type of conductivity and concentration of charge carriers

Correct Answer : type of conductivity and concentration of charge carriers

Explanation : If a potential difference is developed across a current carrying metal strip when the strip is placed in transverse magnetic field.

Hall effect is very weak in metals, but it is large semiconductors.

71 .

Which of these has highly doped p and n region?

A)

PIN diode

B)

Photodiode

C)

Tunnel diode

D)

Schottky diode

Correct Answer : Tunnel diode

Explanation : Tunnel diode has heavily doped p and n regions leading to very thin depletion layer.

72 .

When a p-n junction is forward biased

A)

the width of depletion layer decreases

B)

the width of depletion layer increases

C)

the current is very small

D)

the majority carriers move away from the junction

Correct Answer : the width of depletion layer decreases

Explanation : Forward voltage decreases the width of depletion layer leading to low resistance.

73 .

Which of the following is false about Fermi-Dirac distribution function f(E) used to understand semiconductors in electronic circuits?

A)

When the temperature decreases f(E) also increases

B)

f(E) doesnâ€™t give the number of energy levels with electrons

C)

f(E) is the probability of finding an electron in an energy level E

D)

f(E) doesnâ€™t give the number of electrons in a given energy level

Correct Answer : When the temperature decreases f(E) also increases

Explanation : Fermi-Dirac distribution function f(E) is the probability of finding an electron in an energy level E. When temperature increases f(E) also increases.

74 .

Mass action law is not valid for which type of semiconductors in electronic devices?

A)

Elemental

B)

Degenerative

C)

Compound

D)

Compensated

Correct Answer : Degenerative

Explanation : Mass action law is related to the concentration of electrons and holes in a semiconductor. Degenerative type semiconductors show similar behavior to metal. So, Mass action law is not valid for them.

75 .

Which of the following is the correct expression of current in an intrinsic semiconductor electronic circuit?

A)

I_Total = I_e + 2I_h

B)

I_Total = 2I_e + I_h

C)

I_Total = I_e – I_h

D)

I_Total = I_e + I_h

Correct Answer : I_Total = I_e + I_h

Explaination : When electric field is applied to an intrinsic semiconductor, electrons and holes move in the opposite direction. So, the total current will be the sum of the current due to electrons and holes.

76 .

Which of the following is wrong about P-N junction diodes used in electronic devices?

A)

They can act as ON-OFF switches

B)

They have three modes of operations

C)

They have dynamic resistance at low-frequency AC voltage

D)

They have diffusion capacitance at high-frequency AC voltage

Correct Answer : They have three modes of operations

Explanation : P-N junction diodes have two modes of operations i.e. forward and reverse bias. Forward bias is called ON switch and reverse bias is called OFF switch.

77 .

What is the conductivity of an extrinsic type semiconductor electronic device at 0K?

A)

zero

B)

minimum

C)

maximum

D)

canâ€™t be determined

Correct Answer : zero

Explanation : At T = 0K, conductivity will be zero because donar level ionization is zero, so no free electron is there in the conduction band. Conductivity is measured when free electrons are present in the conduction band for conduction.

78 .

What is the conductivity of an extrinsic type semiconductor electronic device at 300K?

A)

Zero

B)

Minimum

C)

Maximum

D)

Canâ€™t be determined

Correct Answer : Maximum

Explanation : At 300k, conductivity is maximum because of complete ionization of dopant levels which causes more free electrons conductivity in the conduction band.

79 .

Which of the following effects is responsible for violating the mass action law in degenerative type semiconductor electronic devices?

A)

Thermal effect

B)

Electronic drift effect

C)

Lattice vibration effect

D)

Bandgap narrowing effect

Correct Answer : Electronic drift effect

Explanation : With a very high amount of doping in degenerative type semiconductors, atoms come closer. For this reason, the interatomic interaction cannot be neglected. So, the effective band gap becomes narrow.

80 .

Which of the following diode is used in ultra-high speed switching electronic circuits?

A)

Zener diode

B)

Schottky diode

C)

Varactor diode

D)

Tunnel diode

Correct Answer : Tunnel diode

Explanation : Due to tunneling, a large number of electrons penetrate through the junction, so a large amount of current is produced. And as we are considering a special diode, we can control its I-V characteristics to improve the switching speed.

81 .

Power diodes are generally

A)

Silicon diodes

B)

Germanium diodes

C)

Either of the above

D)

None of the above

Correct Answer : Silicon diodes

82 .

Silicon is not suitable for fabrication of light emitting diodes because it is

A)

Wideband gap semiconductor

B)

Narrowband gap semiconductor

C)

Direct band gap semiconductor

D)

An indirect band gap semiconductor

Correct Answer : An indirect band gap semiconductor

83 .

Which variety of copper has the best conductivity?

A)

Hard drawn copper

B)

Pure annealed copper

C)

Induction hardened copper

D)

Copper containing traces of silicon

Correct Answer : Pure annealed copper

84 .

Free electrons exist in

A)

First band

B)

Second band

C)

Third band

D)

Conduction band

Correct Answer : Conduction band

85 .

In a half wave rectifier, the load current flows

A)

For full cycle

B)

For less than fourth cycle

C)

Only for the positive half cycle of the input signal

D)

Only for the negative half cycle of the input signal

Correct Answer : Only for the positive half cycle of the input signal

86 .

The carriers of n channel JFET are

A)

holes

B)

free electrons

C)

free electrons or holes

D)

free electrons and holes

Correct Answer : free electrons

87 .

The depletion layer around p-n junction in JFET consists of

A)

hole

B)

electron

C)

immobile charges

D)

None of the above

Correct Answer : immobile charges

88 .

When a p-n-p transistor is properly biased to operate in active region the holes from emitter.

A)

recombine with electrons in base

B)

recombine with electrons in emitter

C)

diffuse through base into collector region

D)

None of the above

Correct Answer : diffuse through base into collector region

89 .

Assertion (A): Silicon is preferred over germanium in manufacture of semiconductor devices.

Reason (R): Forbidden gap in silicon is more than that in germanium.

A)

A is true but R is false

B)

A is false but R is true

C)

Both A and R are true but R is not a correct explanation of A

D)

Both A and R are true and R is correct explanation of A

Correct Answer : Both A and R are true and R is correct explanation of A

Explaination : Wider forbidden gap in silicon makes it less sensitive to temperature than germanium.

90 .

At room temperature a semiconductor material is

A)

conductor

B)

slightly conducting

C)

perfect insulator

D)

Any of the above

Correct Answer : slightly conducting

Explanation : At 0 K a semiconductor is perfect insulator. At room temperature it is slightly conducting.

91 .

A diode is operating in forward region and the forward voltage and current are v = 3 + 0.3 sin ωt (volts) and i = 5 + 0.2 sin ωt (mA). The average power dissipated is

A)

1.5 mW

B)

15 mW

C)

about 15 mW

D)

about 1.5 mW

Correct Answer : about 15 mW

Explaination : The contribution of sine terms to power dissipation is zero.

92 .

For BJT transistor. The maximum power dissipation is specified as 350 mW if ambient temperature is 25°C. If ambient temperature is 60°C the maximum power dissipation should be limited to about

A)

100 mW

B)

250 mW

C)

450 mW

D)

600 mW

Correct Answer : 250 mW

Explaination : 350 - 2.5 (60 - 25) ∼ 250 mW.

93 .

The concentration of minority carriers in a semiconductor depends mainly on

A)

temperature

B)

the applied bias

C)

the extent of doping

D)

None of the above

Correct Answer : temperature

Explanation : Minority carriers are generated due to thermal excitation.

94 .

Which of the following has highest conductivity?

A)

Silver

B)

Tungsten

C)

Platinum

D)

Aluminium

Correct Answer : Silver

Explanation : Silver has highest conductivity (and lowest resistivity) in all metals.

95 .

In a bipolar junction transistor the base region is made very thin so that

A)

base can be easily biased

B)

base can be easily fabricated

C)

electric field gradient in base is high

D)

recombination in base region is minimum

Correct Answer : recombination in base region is minimum

Explanation :

Since recombination in base region is minimum, I - I_E.

96 .

Compared to bipolar junction transistor, a JFET has

A)

higher voltage gain

B)

lower input impedance

C)

high input impedance and high voltage gain

D)

high input impedance and low voltage gain

Correct Answer : high input impedance and low voltage gain

Explanation : JFET is voltage controlled device. Therefore its input impedance is high. But voltage gain is lower than in BJT.

97 .

The drain characteristics of JFET in operating region, are

A)

almost flat

B)

inclined upwards

C)

inclined downwards

D)

inclined upwards or downwards

Correct Answer : almost flat

Explanation : The drain current is almost constant. Therefore, characteristics is flat.

98 .

As temperature increases

A)

the forbidden energy gap in silicon and germanium increase

B)

the forbidden energy gap in silicon and germanium decrease

C)

the forbidden energy gap in silicon increases while that in germanium decreases

D)

the forbidden energy gap in silicon decreases while that in germanium decreases

Correct Answer : the forbidden energy gap in silicon and germanium decrease

Explanation : Therefore, conductivity increases.

99 .

When a reverse bias is applied to a p-n junction, the width of depletion layer.

A)

decreases

B)

remains the same

C)

increases

D)

may be increase or decrease

Correct Answer : increases

Explanation : Therefore, the resistance is very high.

100 .

Which of the following devices has a silicon dioxide layer?

A)

JFET

B)

MOSFET

C)

Tunnel diode

D)

NPN transistor

Correct Answer : MOSFET

Explanation : The SiO2 layer provides very high input impedance.

101 .

Which statement is false as regards holes

A)

Holes and electrons recombine

B)

Holes constitute positive charges

C)

Holes exist only in semiconductors

D)

Holes exist in conductors as well as semiconductors

Correct Answer : Holes exist in conductors as well as semiconductors

Explanation : Holes do not exist in conductors.

102 .

Photo electric emission can occur only if

A)

wave length of incident radiation is less than threshold value

B)

wave length of incident radiation is equal to threshold value

C)

frequency of incident radiation is less than threshold frequency

D)

None of the above

Correct Answer : wave length of incident radiation is less than threshold value

Explanation : The frequency of incident radiation has to be more than threshold value. Wavelength is inversely proportional to frequency.

Therefore wavelength of incident radiation must be less than threshold value.

103 .

In a piezoelectric crystal, application of a mechanical stress would produce

A)

shift in the Fermi level

B)

magnetic Dipoles in the crystal

C)

electric polarization in the crystal

D)

plastic deformation of the crystal

Correct Answer : electric polarization in the crystal

Explanation : Commonly material used as piezoelectric crystal is Barium Nitrate. Generally ferroelectric crystals and piezoelectric.

104 .

The value of a in a transistor

A)

is about 0.1

B)

is about 0.4

C)

is always equal to 1

D)

is less than 1 but more than 0.9

Correct Answer : is less than 1 but more than 0.9

Explanation : A is about 0.98.

105 .

Which of these has 3 layers?

A)

PIN diode

B)

Zener diode

C)

Photo diode

D)

Schottky diode

Correct Answer : PIN diode

Explanation : p layer, i layer and n layer.

106 .

For an P-channel enhancement type MOSFET determine the drain current if K = 0.278 x 10^-3A/V², V_GS = -4V, V_T = -2V, Voltage equivalent at 27°C = 26 mV.

A)

0.751 mA

B)

1.11 mA

C)

10 mA

D)

46.98 mA

Correct Answer : 1.11 mA

Explaination :

Drain current I_d = k (|V_gs| - |V_T|)²

= 0.278 x 10^-3(4 - 2)²

= 1.11 mA.

107 .

The skin depth of copper is found to be 66 mm at 1 MHz at a certain temperature. At the same temperature and at 2 MHz, the skin depth would be approximately

A)

33 μm

B)

47 μm

C)

92 μm

D)

1.22 μm

Correct Answer : 47 μm

108 .

Which of the following diode is used in adjustable band pass filter electronic circuits?

A)

Zener diode

B)

Tunnel diode

C)

Varactor diode

D)

Schottky diode

Correct Answer : Varactor diode

Explanation : Band pass filter depends upon the value of the resistance and capacitance. In varactor diode, we can obtain capacitance by varying the input voltage. As capacitance becomes adjustable, it can be considered as an adjustable band pass filter.

109 .

Forbidden Energy gap (EG) of a semiconductor in electronic devices depends on which of the following factors?

A)

Electron affinity

B)

Interatomic distance

C)

Material constant

D)

Recombination and Generation

Correct Answer : Interatomic distance

Explanation : Forbidden energy gap (EG) of a semiconductor is directly proportional to the bond strength. And bond strength depends on the interatomic distance.

110 .

Which of the following is the correct order of turn-off times?

A)

MOSFET < BJT < IGBT < SCR

B)

MOSFET < IGBT < BJT < SCR

C)

SCR < BJT < IGBT < MOSFET

D)

BJT < MOSFET < IGBT < SCR

Correct Answer : MOSFET < BJT < IGBT < SCR

Explaination : Electronic devices like MOSFET have the lowest turn-off times (nanoseconds). BJT has turn-off times in between nanoseconds to microseconds. IGBT and SCR have turn-off times of about 1 and 5 microseconds respectively.

111 .

Which of the following type of transistor is preferred in digital and analog electronic circuits?

A)

BJT

B)

FET

C)

JFET

D)

MOSFET

Correct Answer : MOSFET

Explanation : MOSFET is preferred in digital and analog electronic circuits because it is faster than all other transistors. Also, it has a very high input impedance.

112 .

Which of the following is true about the depletion layer channel in an NMOS electronic circuit?

A)

Inverted charge remain constant

B)

Potential in the channel decreases from source to drain

C)

Inverted change in the channel decreases from source to drain

D)

Inverted change in the channel increases from source to drain

Correct Answer : Inverted change in the channel decreases from source to drain

Explanation : When the depletion layer starts moving into the channel, due to the reverse bias of drain and substrate voltage, the inverted charge in the channel decreases from source to drain.

113 .

Which of the following is true about Zener diode?

A)

It is lightly doped

B)

It is used in forward bias

C)

It has avalanche breakdown

D)

It is mostly used in voltage regulator electronic circuits

Correct Answer : It is mostly used in voltage regulator electronic circuits

Explanation : Zener diode is a heavily doped diode. It is used in reverse bias. It has Zener breakdown. It is used in voltage regulators because it passes an excess amount of current in breakdown mode by maintaining constant voltage across the load.

114 .

In which region does BJT act as the OFF switch in electronic circuits?

A)

Active

B)

Cut-off

C)

Saturation

D)

Reverse saturation

Correct Answer : Saturation

Explanation : In the saturation region, the emitter-base junction is forward biased, the collector-base junction is also forward biased. This is the operating mode when no current flows through BJT.

115 .

How many free electrons does a p type semiconductor has?

A)

Only those produced by doping

B)

Only those produced by thermal energy

C)

Those produced by doping as well as thermal energy

D)

Any of the above

Correct Answer : Only those produced by thermal energy

116 .

Light dependent resistors are

A)

Intrinsic semiconductor

B)

Highly doped semiconductor

C)

Lightly doped semiconductor

D)

Either (A) or (B)

Correct Answer : Lightly doped semiconductor

117 .

In a bipolar transistor, the emitter base junction has

A)

Forward bias

B)

Zero bias

C)

Reverse bias

D)

Zero or reverse bias

Correct Answer : Forward bias

118 .

The depletion layer width of Junction

A)

Increases with heavy doping

B)

Decreases with light doping

C)

Is independent of applied voltage

D)

Is increased under reverse bias

Correct Answer : Is increased under reverse bias

119 .

An intrinsic silicon sample has 1 million free electrons at room temperature. As the temperature is increased

A)

The number of free electrons increases

B)

The number of free electrons and holes increase by the same amount

C)

The number of free electrons increases but the number of holes decreases

D)

The number of free electrons and holes increase but not by the same amount

Correct Answer : The number of free electrons and holes increase by the same amount

120 .

If too large current passes through the diode

A)

Diode will emit light

B)

All electrons will leave

C)

All holes will freeze

D)

Excessive heat may damage the diode

Correct Answer : Excessive heat may damage the diode

121 .

Which of the following has highest resistivity?

A)

Air

B)

Mica

C)

Mineral oil

D)

Paraffin wax

Correct Answer : Air

122 .

A semiconductor diode is biased in forward direction and carrying current I. The current due to holes in p material is

A)

I

B)

0

C)

less than I

D)

0.5

Correct Answer : less than I

Explanation : Small current due to minority carriers also. Therefore hole current is less than.

123 .

Between which regions does BJT act like switch?

A)

Saturation and active

B)

Cut off and saturation

C)

Cut off and forward active

D)

Forward active and cut off

Correct Answer : Cut off and saturation

Explanation : In cut off mode a BJT is an open switch and in saturation mode it is a closed switch.

124 .

Light dependent resistor is

A)

photo voltaic device

B)

photo resistive device

C)

photo emissive device

D)

Either (A) or (C)

Correct Answer : photo resistive device

Explanation : Resistance of LDR depends on light.

125 .

The breakdown voltage in a zener diode

A)

is very small

B)

may destroy the diode

C)

is almost constant

D)

decreases with increase in current

Correct Answer : is almost constant

Explanation : Therefore, it is used in voltage regulator circuits.

126 .

A varactor diode is used for

A)

tuning

B)

rectification

C)

amplification

D)

rectification and amplification

Correct Answer : tuning

Explanation : Its voltage dependent capacitance is used for tuning.

127 .

Assertion (A) : When VDS is more than rated value the drain current in a JFET is very high.

Reason (R) : When VDS is more than rated value, avalanche breakdown occurs.

A)

A is true but R is false

B)

A is false but R is true

C)

Both A and R are true and R is correct explanation of A

D)

Both A and R are true but R is not a correct explanation of A

Correct Answer : Both A and R are true and R is correct explanation of A

Explaination : Avalanche breakdown causes high current.

128 .

In which material do conduction and valence bands overlap

A)

insulators

B)

conductors

C)

both conductor and semiconductor

D)

semiconductors

Correct Answer : conductors

Explanation : This is the reason for high conductivity of conductors.

129 .

For a photoconductor with equal electron and hole mobilities and perfect ohmic contacts at the ends, an increase in illumination results in

A)

a change in S.C. current

B)

a change in O.C. voltage

C)

an increase in resistance

D)

a decrease in resistance

Correct Answer : a decrease in resistance

Explanation : Increase in illumination reduces resistance of a photoconductor.

130 .

The number of p-n junctions in a semiconductor diode are

A)

0

B)

1

C)

2

D)

1 or 2

Correct Answer : 1

Explanation : Semiconductor diode has one p-n junction, BJT has two and SCR has three p-n junctions.

131 .

When a diode is not conducting, its bias is

A)

zero

B)

reverse

C)

forward

D)

zero or reverse

Correct Answer : zero or reverse

Explanation : Diode conducts only when forward biased. There is no conduction when bias is zero or reverse.

132 .

The SCR would be turned OFF by voltage reversal of applied anode-cathode ac supply of frequency of

A)

5 kHz

B)

15 kHz

C)

20 kHz

D)

30 kHz

Correct Answer : 5 kHz

Explanation : For inverter grade SCR, typical turn off time (t_off) is 5 to 50 μsec while 50 to 100 μsec for converter grade SCR.

Hence supply frequency of 5 kHz will turn off the SCR by voltage reversal because 1/5KHz = 200 μsec.

133 .

The number of valence electrons in a donor atom is

A)

2

B)

3

C)

4

D)

5

Correct Answer : 5

Explanation : Therefore, it can donate one electron.

134 .

A Varactor diode has

A)

a fixed inductance

B)

a fixed capacitance

C)

a voltage variable capacitance

D)

a current variable inductance

Correct Answer : a voltage variable capacitance

Explanation : The applied bias governs the width of depletion layer. Therefore, capacitance varies with bias.

135 .

The most important set of specifications of transformer oil includes

A)

flash point and viscosity

B)

dielectric strength, flash point and viscosity

C)

dielectric strength and viscosity

D)

dielectric strength and flash point

Correct Answer : dielectric strength, flash point and viscosity

Explanation : Oil used in transformer work as cooling as well as dielectric strength.

136 .

A voltage of 9 V is applied in forward direction to a semiconductor diode in series with a load resistance of 1000 Ω. The voltage across the load resistance is zero. It indicates that

A)

diode is short circuited

B)

diode is open circuited

C)

resistor is open circuited

D)

diode is either o.c or s.c

Correct Answer : diode is open circuited

Explaination : Since there is no voltage across load resistor, the current is zero and diode is open-circuit. If diode is short- circuited or resistor is open-circuited almost 9 V will appear across resistor.

137 .

If the drift velocity of holes under a field gradient of 100 V/m in 5 m/s, their mobility (in SI units) is

A)

0.05

B)

0.5

C)

50

D)

500

Correct Answer : 0.05

138 .

The derating factor for a BJT transistor is about

A)

0.5 mW/Â°C

B)

2.5 mW/Â°C

C)

10 mW/Â°C

D)

25 mW/Â°C

Correct Answer : 2.5 mW/Â°C

Explanation : For every 1°C rise in ambient temperature the power dissipation must be reduced by 2.5 mW so that transistor is safe.

139 .

An intrinsic silicon sample has 2 million free electrons. The number of holes in the sample is

A)

2 million

B)

almost zero

C)

more than 2 million

D)

less than 2 million

Correct Answer : 2 million

Explanation : In intrinsic semiconductor, the number of free electrons is equal to number of holes.

140 .

In an n type semiconductor

A)

number of free electrons and holes are equal

B)

number of holes is greater than the number of free electrons

C)

number of free electrons is much greater than the number of holes

D)

number of free electrons may be equal or less than the number of holes

Correct Answer : number of free electrons is much greater than the number of holes

Explanation : Therefore, in n type semiconductor electrons are majority carriers.

141 .

In an n type semiconductor the fermi level is 0.35 eV below the conduction band, the concentration of donor atoms is increased to three times. The new position of Fermi level will be

A)

0.35 eV below conduction band

B)

about 0.32 eV below conduction band

C)

about 0.1 eV below conduction band

D)

about 0.32 eV above conduction band

Correct Answer : about 0.32 eV below conduction band

Explaination : Therefore, conductivity increases.

142 .

In a bipolar transistor

A)

recombination in base regions of both n-p-n and p-n-p transistor is low

B)

recombination in base regions of both n-p-n and p-n-p transistors is high

C)

recombination in base region of n-p-n transistor is low but that in p-n-p transistor is high

D)

recombination in base region of p-n-p transistor is low but that in n-p-n transistor is high

Correct Answer : recombination in base regions of both n-p-n and p-n-p transistor is low

Explanation : Base is very thin and therefore recombination is minimum in both p-n-p and n-p-n transistors.

143 .

The number of doped regions in a bipolar junction transistor is

A)

1

B)

2

C)

3

D)

4

Correct Answer : 3

Explanation : p, n, p or n, p, n.

144 .

GaAs has an energy gap 1.43 eV the optical cut off wavelength of GaAs would lie in the

A)

visible region of the spectrum

B)

infrared region of the spectrum

C)

ultraviolet region of the spectrum

D)

for ultraviolet region of the spectrum

Correct Answer : infrared region of the spectrum

Explanation : GaAs has very large band gap and high carrier mobility.

145 .

Which of the following is basically a voltage controlled capacitance?

A)

LED

B)

Diode

C)

Zener diode

D)

Varactor diode

Correct Answer : Varactor diode

Explanation : Therefore, varactor is used for tuning in TV.

146 .

When the i-v curve of a photodiode passes through origin the illumination is

A)

zero

B)

minimum

C)

maximum

D)

equal to rated value

Correct Answer : zero

Explanation : i is plotted on y-axis and v on x-axis. When passing through origin current can be zero only.

147 .

In which device does the extent of light controls the conduction

A)

LED

B)

photovoltaic cell

C)

photo electric relay

D)

photo sensitive device

Correct Answer : photo sensitive device

Explanation : The resistance of photosensitive device depends on the light.

148 .

Which of the following expressions represents the correct distribution of the electrons in the conduction band? (gc(E)=density of quantum states, fF(E)=Fermi dirac probability

A)

n(E)=gc(E)*fF(E)

B)

n(E)=gc(E)*fF(-E)

C)

n(E)=gc(-E)*fF(E)

D)

n(E)= gc(-E)*fF(-E)

Correct Answer : n(E)=gc(E)*fF(E)

Explaination : The distribution of the electrons in the conduction band is given by the product of the density into Fermi-dirac distribution.

149 .

Which of the following expressions represent the Fermi probability function?

A)

fF(E)=exp(-[EF-E]/KT)

B)

fF(E)=exp([E-EF]/KT)

C)

fF(E)=exp(-[E-EF]/KT)

D)

fF(E)=exp(-[EF-E]/KT)

Correct Answer : fF(E)=exp(-[EF-E]/KT)

Explanation : It is the correct formula for the Fermi probability function.

150 .

What is the difference between the practical value and theoretical value of ni?

A)

Factor of 1

B)

Factor of 2

C)

Factor of 3

D)

Factor of 4

Correct Answer : Factor of 2

Explanation : This is practically proved.

151 .

In which of the following semiconductor, the concentration of the holes and electrons is equal?

A)

Extrinsic

B)

Elemental

C)

Intrinsic

D)

Compound

Correct Answer : Intrinsic

Explanation : In the intrinsic semiconductor, ni=pi that is the number of the electrons is equal to the number of the holes. Whereas in the extrinsic conductor ni is not equal to pi.

152 .

What is the SI unit of conductivity?

A)

m

B)

â„¦

C)

â„¦m

D)

(â„¦m)-1

Correct Answer : (â„¦m)-1

Explanation : The formula of the conductivity is the σ=1/ρ.

So, the unit of resistivity is â„¦m.

Now, the unit of conductivity becomes the inverse of resistivity.

153 .

Which of the following expressions doesnâ€™t represent the correct formula for Drift current density?

A)

J=ÏƒE

B)

J=ÂµE

C)

J=qnÂµE

D)

None of the above

Correct Answer : J=ÂµE

Explanation : The following formulae represent the correct expression for drift current density,
J=σE
And J=qnµE.

154 .

In which range of temperature, freeze out point begins to occur?

A)

Lower range

B)

Middle range

C)

Higher range

D)

None of the above

Correct Answer : Lower range

Explanation : At lower range of temperature, the concentration and conductivity decreases with lowering of the temperature.

155 .

What is the electric field when the voltage applied is 5V and the length is 100cm?

A)

0.5V/m

B)

5V/m

C)

50V/m

D)

None of the above

Correct Answer : 50V/m

Explanation : E=V/L=5/100cm=5V/m.

156 .

Calculate the average random thermal energy at T=300K?

A)

38eV

B)

3.8eV

C)

0.38eV

D)

0.038eV

Correct Answer : 0.038eV

Explanation : Average random thermal energy=3/2*k*T=0.038eV.

157 .

If the positive terminal of the battery is connected to the anode of the diode, then it is known as

A)

Forward biased

B)

Equilibrium

C)

Reverse biased

D)

Schottky barrier

Correct Answer : Forward biased

Explanation : When a positive terminal is connected to the anode, the diode is forward biased which lets the flow of the current in the circuit.

158 .

During reverse bias, a small current develops known as

A)

Active current

B)

Reverse current

C)

Forward current

D)

Reverse saturation current

Correct Answer : Reverse saturation current

Explanation : When the diode is reverse biased, a small current flows between the p-n junction which is of the order of the Pico ampere. This current is known as reverse saturation current.

159 .

What is the maximum electric field when V_bi=2V , V_R=5V and width of the semiconductor is 7cm?

A)

-100V/m

B)

-200V/m

C)

100V/m

D)

200V/m

Correct Answer : -200V/m

Explaination : Emax=-2(V_bi+V_R)/W
=-2(2+5)/ (7*10^-2)
=-200V/m.

160 .

The static resistance R of the diode is given by __________

A)

V*I

B)

V/I

C)

V+I

D)

V-I

Correct Answer : V/I

Explanation : According to Ohms law the electric current in the circuit is directly proportion to voltage and inversely proportional to resistance so, R=V/I.

161 .

In the volt ampere characteristics of the diode, the slope of the line joining the operating point to the origin at any point is equal to reciprocal of the _________

A)

voltage

B)

current

C)

resistance

D)

conductance

Correct Answer : resistance

Explaination : In the diode’s volt ampere characteristics, the line joining the operating point and the origin, at any point of the line is equal to the conductance so, it is reciprocal of the resistance.

162 .

At room temperature (V_T = 26) what will be the approximate value of r when n=1 and I=100mA?

A)

2.6 ohms

B)

26 ohms

C)

260 ohms

D)

2600 ohms

Correct Answer : 260 ohms

Explaination : We know that R= (n*V_T) /I, by substituting the value of n, V_T, I we get R= 260 ohms, (1*26)/100*10^-3 = 260 ohms.

163 .

In the diode volt ampere characteristics what will be the resistance if a slope is drawn between the voltages 50 to 100 and corresponding current 5 to 10?

A)

5 ohms

B)

10 ohms

C)

50 ohms

D)

100 ohms

Correct Answer : 10 ohms

Explaination : We know that, in volt ampere characteristics the resistance is equal to the reciprocal of the line joining the origin and operating point, R = dV/dI, by substituting the value of dV and dI we get R= 10ohms.

164 .

A diode will behave as an open circuit if the voltage in the circuit is less than __________

A)

cut off voltage

B)

leakage voltage

C)

threshold voltage

D)

saturation voltage

Correct Answer : threshold voltage

Explanation : The diode made up of semiconductor has a certain threshold voltage only after which it behave as closed circuit in the sense it performs some operation if the threshold voltage is greater than the voltage in circuit.

165 .

What will be the approximate value of thermal voltage of diode?

A)

25mV at 180K

B)

25mV at 300K

C)

30mV at 180K

D)

30mV at 300K

Correct Answer : 25mV at 300K

Explanation : We know that the thermal voltage of diode is approximately equal to room temperature which is 300K then for all practical purpose the thermal voltage of diode is taken as 25mV so it will be 25mV at 300K.

166 .

What will be the diode resistance if the current in the circuit is zero?

A)

0 ohms

B)

0.3 ohms

C)

0.7 ohms

D)

1 ohms

Correct Answer : 0 ohms

Explanation : When the current in the circuit is zero there will be no flow of charges to resist hence the diode resistance will be zero.

167 .

Which of these following is not a characteristic of an ideal diode?

A)

Perfect insulator when reverse bias

B)

Perfect conductor when forward bias

C)

Zero voltage across it when forward bias

D)

Zero current through it when forward bias

Correct Answer : Zero current through it when forward bias

Explanation : The diode acts as an ideal diode when it is a perfect conductor and has zero voltage across it during forward bias, a perfect insulator and zero current through it during reverse bias.

168 .

Compared to a PN junction with N_A=10¹⁴/CM³, which one of the following is true for N_A=N_D= 10²⁰/CM³?

A)

depletion capacitance increases

B)

depletion capacitance decreases

C)

depletion capacitance remains same

D)

depletion capacitance can’t be predicted

Correct Answer : depletion capacitance increases

Explaination : We know, C_T=Aε/W and
W ∝ (1/N_A+1/N_D)^1/2. So, C_T ∝ (1/N_A+1/N_D)^-1/2
So when N_A and N_D increases, depletion capacitance C_T increases.

169 .

The built in capacitance V₀ for a step graded PN junction is 0.75V. Junction capacitance C_j at reverse bias when V_R=1.25V is 5pF. The value of C_j when V_R=7.25V is?

A)

0.1pF

B)

1pF

C)

1.7pF

D)

2.5Pf

Correct Answer : 2.5Pf

Explaination : We know, C_j1/ C_j2=[(V₀+V_R2)/(V₀+V_R2)]^1/2
So, C_j2=C_j1/ {(0.75+7.25)/(0.75+1.25)}^1/2 we get C_j2=C_j1 /2 =5/2=2.5Pf.

170 .

The diffusion capacitance of a PN junction _______

A)

decreases with increasing current and increasing temperature

B)

increasing with increasing current and increasing temperature

C)

decreases with decreasing current and increasing temperature

D)

doesnot depend on current and temperature

Correct Answer : decreases with decreasing current and increasing temperature

Explanation : C_D =τ I /n₀ V_T
Where, I is the current and VT is temperature factor. The diffusion capacitance is directly proportional to current and indirectly proportional to the temperature.

171 .

Transition capacitance is also called as _______

A)

diffusion capacitance

B)

depletion capacitance

C)

resistive capacitance

D)

conductance capacitance

Correct Answer : depletion capacitance

Explanation : Transition capacitance occurs in reverse bias. We obtain a depletion layer in that case. Hence it’s also called as depletion capacitance. The diffusion capacitance occurs in forward bias.

172 .

For an ideal diode which of the following is true?

A)

It does not allow the flow of current in reverse bias

B)

It allows the passage of current in the forward bias with zero potential drop across the diode

C)

All of the mentioned

D)

None of the above

Correct Answer : All of the mentioned

Explanation : Both of the facts mentioned hold true for an ideal operational amplifier.

173 .

Diodes can be used in the making of

A)

Rectifiers

B)

LED lamps

C)

Logic gates

D)

All of the above

Correct Answer : All of the above

Explanation : Diodes are used to make rectifiers (full wave or half wave rectifiers are the most common examples), LED lamps uses diodes (diodes are generally doped for their use in this purpose) and logic gates can also be made using diodes using the fact that diodes are conducting only in the forward biased configuration.

174 .

The units frequently used to measure the forward bias and reverse bias current of a diode are

A)

mA and ÂµA respectively

B)

mA and mA respectively

C)

ÂµA and ÂµA respectively

D)

ÂµA and mA respectively

Correct Answer : mA and ÂµA respectively

Explanation : The currents in forward bias is generally in MA and in the reverse bias it is very small and is generally measured in µA.

175 .

Which of the following isn't a type of rectifier?

A)

Peak Rectifier

B)

Bridge Rectifier

C)

Precision Half-wave Rectifier

D)

None of the above

Correct Answer : None of the above

Explanation : All of the mentioned are different types of a rectifier.

176 .

For a half wave or full wave rectifier the Peak Inverse Voltage of the rectifier is always

A)

Equal to the input voltage

B)

Smaller than the input voltage

C)

Greater than the input voltage

D)

Greater than the input voltage for full wave rectifier and smaller for the half wave rectifier

Correct Answer : Smaller than the input voltage

Explanation : The peak input voltage is smaller than the input voltage due to the presence of diode(s). A single diode reduces the output voltage by approximately 0.7V.

177 .

Bridge rectifier is an alternative for

A)

Peak rectifier

B)

Half wave rectifier

C)

Full wave rectifier

D)

None of the above

Correct Answer : Full wave rectifier

Explanation : Bridge rectifier is a better alternative for a full wave rectifier.

178 .

Which of the following is true for a bridge rectifier?

A)

The output voltage for the center tapped rectifier is lower than the identical bridge rectifier

B)

A transistor of higher number of coil is required for center tapped rectifier than the identical bridge rectifier

C)

The peak inverse voltage or PIV for the bridge rectifier is lower when compared to an identical center tapped rectifier

D)

All of the above

Correct Answer : All of the above

Explanation : All of the given statements are true for a bridge rectifier.

179 .

The diode rectifier works well enough if the supply voltage is much than greater than 0.7V. For smaller voltage (of few hundreds of millivolt) input which of the following can be used?

A)

Superdiode

B)

Peak rectifier

C)

Precision rectifier

D)

None of the above

Correct Answer : Superdiode

Explaination : For the supply voltages less than 0.7V super diodes are used.

180 .

Efficiency of a centre tapped full wave rectifier is ________

A)

46%

B)

50%

C)

70%

D)

81.2%

Correct Answer : 81.2%

Explanation : Efficiency of a rectifier is the effectiveness to convert AC to DC. It’s obtained by taking ratio of DC power output to maximum AC power delivered to load. It’s usually expressed in percentage. For centre tapped full wave rectifier, it’s 81.2%.

181 .

A full wave rectifier delivers 50W to a load of 200â„¦. If the ripple factor is 2%, calculate the AC ripple across the load.

A)

1V

B)

2V

C)

3V

D)

4V

Correct Answer : 2V

Explanation : We know that, P_DC=V_DC²/R_L. So, V_DC=(P_DC*RL)^1/2=10000^1/2=100V.
Here, ϒ=0.02
ϒ=V_AC/V_DC=V_AC/100.So, V_AC=0.02*100=2V.

182 .

In a centre tapped full wave rectifier, R_L=1Kâ„¦ and for diode Rf=10â„¦. The primary voltage is 800sinωt with transformer turns ratio=2. The ripple factor will be _________

A)

26%

B)

48%

C)

54%

D)

81%

Correct Answer : 48%

Explaination : The ripple factor ϒ= [(I_RMS/I_AVG)² – 1]^1/2. I_RMS =I_m /√2=V_m/(R_f+R_L)√2=200/1.01=198.
(Secondary line to line voltage is 800/2=400. Due to centre tap V_m=400/2=200)
I_RMS=198/√2=140mA, I_AVG=2*198/π=126mA. ϒ=[(140/126)²-1]^1/2=0.48. So, ϒ=48%.

183 .

If input frequency is 50Hz for a full wave rectifier, the ripple frequency of it would be _________

A)

25Hz

B)

50Hz

C)

100Hz

D)

500Hz

Correct Answer : 100Hz

Explanation : In the output of the centre tapped rectifier, one of the half cycle is repeated. The frequency will be twice as that of input frequency. So, it’s 100Hz.

184 .

Transformer utilization factor of a centre tapped full wave rectifier is_________

A)

0.623

B)

0.625

C)

0.678

D)

0.693

Correct Answer : 0.693

Explanation : Transformer utilisation factor is the ratio of AC power delivered to load to the DC power rating. This factor indicates effectiveness of transformer usage by rectifier. For a half wave rectifier, it’s low and equal to 0.693.

185 .

In a centre tapped full wave rectifier, the input sine wave is 250sin100t. The output ripple frequency will be ________

A)

25Hz

B)

50Hz

C)

100Hz

D)

200Hz

Correct Answer : 100Hz

Explanation : The equation of sine wave is in the form V_msinωt. So, by comparing we get ω=100. Frequency, f =ω/2=50Hz. The output of centre tapped full wave rectifier has double the frequency of inpu. Hence, f_out = 100Hz.

186 .

In a shunt capacitor filter, the mechanism that helps the removal of ripples is_______

A)

The property of capacitor to store electrical energy

B)

The current passing through the capacitor

C)

Uniform charge flow through the rectifier

D)

The voltage variations produced by shunting the capacitor

Correct Answer : The property of capacitor to store electrical energy

Explanation : Filtering is frequently done by shunting the load with capacitor. It depends on the fact that a capacitor stores energy when conducting and delivers energy during non conduction. Throughout this process, the ripples are eliminated.

187 .

The cut-in point of a capacitor filter is_________

A)

The instant at which the conduction stops

B)

The instant at which the conduction starts

C)

The time after which the output is not filtered

D)

The time during which the output is perfectly filtered

Correct Answer : The instant at which the conduction starts

Explanation : The capacitor charges when the diode is in ON state and discharges during the OFF state of the diode. The instant at which the conduction starts is called cut-in point. The instant at which the conduction stops is called cut-out point.

188 .

The rectifier current is a short duration pulses which cause the diode to act as a______

A)

Mixer

B)

Switch

C)

Oscillator

D)

Voltage regulator

Correct Answer : Switch

Explanation : The diode permits charge to flow in capacitor when the transformer voltage exceeds the capacitor voltage. It disconnects the power source when the transformer voltage falls below that of a capacitor.

189 .

A half wave rectifier, operated from a 50Hz supply uses a 1000µF capacitance connected in parallel to the load of rectifier. What will be the minimum value of load resistance that can be connected across the capacitor if the ripple% not exceeds 5?

A)

114.87â„¦

B)

115.47â„¦

C)

167.98â„¦

D)

451.35â„¦

Correct Answer : 115.47â„¦

Explaination : For a half wave filter,
ϒ=1/2√3 fCR_L=1/2√3*50*10^-3*R_L
R_L=10³/5√3=115.47â„¦.

190 .

A full wave rectifier uses a capacitor filter with 500µF capacitor and provides a load current of 200mA at 8% ripple. Calculate the dc voltage.

A)

11.98V

B)

14.43V

C)

15.56V

D)

20.43V

Correct Answer : 14.43V

Explaination : The ripple factor ϒ=I_L/ 4√3 fCV_DC
V_DC=200*10^-3/ 4√3 *50*500*8
=14.43.

191 .

Which of the following are true about capacitor filter?

A)

It is electrolytic

B)

It is connected in parallel to load

C)

It helps in storing the magnetic energy

D)

It is also called as capacitor output filter

Correct Answer : It is electrolytic

Explanation : The rectifier may be full wave or half wave. The capacitors are usually electrolytic even though they are large in size.

192 .

A shunt capacitor of value 500µF fed rectifier circuit. The dc voltage is 14.43V. The dc current flowing is 200mA. It is operating at a frequency of 50Hz. What will be the value of peak rectified voltage?

A)

11.43V

B)

15.98V

C)

16.43V

D)

18.67V

Correct Answer : 16.43V

Explaination : We know, V_m=V_dc+I_dc/4fC
=14.43+ {200/ (200*500)} 10³
=14.43+2=16.43V.

193 .

The output, V-I characteristics of an Enhancement type MOSFET has

A)

Only an ohmic region

B)

Only a saturation region

C)

An ohmic region at low voltage value followed by a saturation region at higher voltages

D)

An ohmic region at large voltage values preceded by a saturation region at lower voltages

Correct Answer : An ohmic region at low voltage value followed by a saturation region at higher voltages

194 .

The sensitivity of human eyes is maximum at

A)

Red portion of spectrum

B)

Violet portion of spectrum

C)

White portion of spectrum

D)

Green portion of spectrum

Correct Answer : Green portion of spectrum

195 .

Which of the following could be the maximum current rating of junction diode by 126?

A)

1 A

B)

10 A

C)

20 A

D)

100 A

Correct Answer : 1 A

196 .

Piezoelectric quartz crystal resonators find application where

A)

Modulation of signal is required

B)

Rectification of the signal is required

C)

Signal amplification is required

D)

Signal frequency control is required

Correct Answer : Rectification of the signal is required

197 .

In the sale of diamonds the unit of weight is carat. One carat is equal to

A)

100 mg

B)

150 mg

C)

200 mg

D)

500 mg

Correct Answer : 200 mg

198 .

Forbidden energy gap in germanium at 0 K is about

A)

0.78 eV

B)

2 eV

C)

5 eV

D)

10 eV

Correct Answer : 0.78 eV

199 .

In a semiconductor diode, the barrier offers opposition to

A)

Holes in P-region only

B)

Free electrons in N-region only

C)

Majority carriers in both regions

D)

Majority as well as minority carriers in both regions

Correct Answer : Majority carriers in both regions

200 .

As compared to bipolar junction transistor, a FET

A)

Is less noisy

B)

Has better thermal stability

C)

Has higher input resistance

D)

All of the above

Correct Answer : All of the above

201 .

Permalloy is_______

A)

A polymer

B)

A variety of stainless steel

C)

A conon-ferrous alloy used in aircraft industry

D)

A nickel an iron alloy having high permeability

Correct Answer : A nickel an iron alloy having high permeability

202 .

Which one of the following is not a characteristic of a ferroelectric material?

A)

No hysteresis

B)

Electric dipole moment

C)

Ferroelectric characteristic only above the curie point

D)

High dielectric constant

Correct Answer : Ferroelectric characteristic only above the curie point

203 .

Hall effect is observed in a specimen when it is carrying current and is placed in a magnetic field. The resultant electric field inside the specimen is

A)

In arbitrary direction

B)

In the direction of current

C)

Antiparallel to magnetic field

D)

Normal to both current and magnetic field

Correct Answer : Normal to both current and magnetic field

204 .

Fermi level is the amount of energy in which

A)

A hole can have at room temperature

B)

An electron can have at room temperature

C)

Must be given to an electron move to conduction band

D)

None of the above

Correct Answer : Must be given to an electron move to conduction band

205 .

When diodes are connected in series to increase voltage rating the peak inverse voltage per junction

A)

should not exceed the breakdown voltage

B)

should not exceed one third the breakdown voltage

C)

should not exceed half the breakdown voltage

D)

may be equal to or less than breakdown voltage

Correct Answer : should not exceed one third the breakdown voltage

206 .

In monolithic ICs, all the components are fabricated by

A)

Diffusion process

B)

Oxidation

C)

Evaporation

D)

None of the above

Correct Answer : Diffusion process

207 .

An increase in junction temperature of a semiconductor diode

A)

causes a large increase in reverse saturation current

B)

does not affect reverse saturation current

C)

causes a small increase in reverse saturation current

D)

may cause an increase or decrease in reverse saturation current depending on rating of diode

Correct Answer : causes a large increase in reverse saturation current

Explanation : Reverse saturation current doubles for every 10°C rise in junction temperature.

208 .

An air gap provided in the iron core of an inductor prevents

A)

flux leakage

B)

hysteresis loss

C)

heat generation

D)

core saturation

Correct Answer : core saturation

209 .

Generally, the gain of a transistor amplifier falls at high frequency due to the

A)

skin effect

B)

coupling capacitor at the I/P

C)

internal capacitance of the device

D)

coupling capacitor at the O/P

Correct Answer : internal capacitance of the device

210 .

A Si sample is doped with a fixed number of group N impurities. The electron density n is measured from 4 K to 1200 k for the sample. Which one of the following is correct?

A)

n increases monotonicaliy with increasing temp

B)

n remains constant over the temperature range

C)

n increases show a peak and then decrease with temperature

D)

n increases first remains constant over a range and again increases with increasing temperature

Correct Answer : n increases monotonicaliy with increasing temp

211 .

The behaviour of a JFET is similar to that of

A)

SCR

B)

PNP transistor

C)

Vacuum triode

D)

NPN transistor

Correct Answer : Vacuum triode

Explanation : Both JFET and vacuum triode are voltage controlled devices.

212 .

If the drift velocity of holes under a field gradient of 100 V/m is 5m/sec. Their mobility is

A)

0.05

B)

0.5

C)

50

D)

500

Correct Answer : 0.05

213 .

What is the effect of cut in voltage on the wave form of output as compared to input in a semiconductor diode?

A)

The duration of output waveform is less than 180Â°

B)

Output voltage is less than input voltage

C)

Output voltage is more than input voltage

D)

Both (A) and (B)

Correct Answer : Both (A) and (B)

Explanation : Since the duration of output waveform is less than 180°, output voltage is less than input voltage.

214 .

As temperature increases the number of free electrons and holes in an intrinsic semiconductor

A)

increases

B)

decreases

C)

remains the same

D)

may increase or decrease

Correct Answer : increases

Explanation : Increase of temperature increases conductivity of semiconductors.increases

215 .

In a reverse biased P-N junction, the current through the junction increases abruptly at

A)

1.2 V

B)

0.72 V

C)

zero voltage

D)

breakdown voltage

Correct Answer : breakdown voltage

216 .

Dielectric strength of polythene is around

A)

10 kV/mm

B)

40 kV/mm

C)

100 kV/mm

D)

140 kV/mm

Correct Answer : 40 kV/mm

217 .

Resistivity of hard drawn copper is

A)

same as that of annealed copper

B)

less than that of annealed copper

C)

more than that of annealed copper

D)

decreasing when temperature increases

Correct Answer : more than that of annealed copper

218 .

The voltage across the secondary of the transformer in a half wave rectifier with a shunt capacitor filter is 50 volts. The maximum voltage that will occur on the reverse biased diode will be

A)

25 V

B)

50 V

C)

88 V

D)

100 V

Correct Answer : 100 V

219 .

For a photoengraving the mask used is

A)

slave mask

B)

working mask

C)

photo mask

D)

master mask

Correct Answer : working mask

Explanation : The mask that is prepared first is called the master mask made from glass substrates covered by thin chromium film.

From the master masks are prepared working masks by contact pointing and used for Photolithography which means Photo engraving.

220 .

In a varactor diode the increase in width of depletion layer results in

A)

decrease in capacitance

B)

increase in capacitance

C)

no change in capacitance

D)

Either (B) or (C)

Correct Answer : decrease in capacitance

Explanation : Capacitance is inversely proportional to distance between plates.

221 .

The work function of a photo surface whose threshold wave length is 1200 A, will be

A)

0.103 eV

B)

0.673 eV

C)

1.03 eV

D)

1.27 eV

Correct Answer : 1.03 eV

222 .

N-type silicon is obtained by doping silicon with

A)

boron

B)

aluminium

C)

germanium

D)

phosphorus

Correct Answer : phosphorus

223 .

When a p-n junction is reverse biased

A)

holes and electrons move towards the junction

B)

holes and electrons move away from the junction

C)

holes move towards junction and electrons move away from junction

D)

holes move away from junction and electrons move towards junction

Correct Answer : holes and electrons move away from the junction

Explanation : Holes and electrons move away from junction and therefore resistance increases to a high value.

224 .

If a sample of germanium and a sample of Si have the impurity density and are kept at room temperature then

A)

resistivity of Si will be higher than of germanium

B)

both will have equal -ve resistivity

C)

both will have equal value of resistivity

D)

resistivity of germanium will be higher than that of silicon

Correct Answer : resistivity of Si will be higher than of germanium

Explanation : Since the majority of charge carrier is better in Ge than in Si, for the same concentration of charge carriers, the conductivity of Ge is higher than that of Si.

225 .

When a large number of atoms are brought together to form a crystal

A)

the energy levels of inner shell electrons are affected appreciably by the presence of other neighbouring atoms.

B)

The energy levels of outer shell electrons are affected appreciably by the presence of other neighbouring atoms.

C)

the energy levels of both inner and outer shell electrons are affected appreciably by the presence of other neighbouring atoms.

D)

None of the above

Correct Answer : The energy levels of outer shell electrons are affected appreciably by the presence of other neighbouring atoms.

Explanation : Inner shell electrons are tightly bound to the nucleus. Their energy levels cannot be affected by presence of other atoms.

226 .

At room temperature the barrier potential in a silicon diode is

A)

0.1 V

B)

0.3 V

C)

0.7 V

D)

1 V

Correct Answer : 0.7 V

Explanation : This 0.7 V is also called cut in voltage. When forward voltage is 0.7 V or less there is no current.

227 .

The cut in voltage of a diode is nearly equal to

A)

barrier potential

B)

applied reverse voltage

C)

applied forward voltage

D)

None of the above

Correct Answer : barrier potential

228 .

A reverse voltage of 18 V is applied to a semiconductor diode. The voltage across the depletion layer is

A)

0 V

B)

0.7 V

C)

10 V

D)

18 V

Correct Answer : 18 V

229 .

Which of the following devices has substrate?

A)

JFET

B)

Depletion Type MOSFET

C)

Enhancement type MOSFET

D)

Both (B) and (C)

Correct Answer : Both (B) and (C)

Explanation : All MOSFETs have substrate.

230 .

In degenerate p type semiconductor material, the Fermi level,

A)

is in conduction band

B)

is in the valence band

C)

is very near conduction band

D)

is at the centre in between valence and conduction bands

Correct Answer : is in the valence band

Explanation : This is due to heavy doping.

231 .

As comparated to an ordinary p-n diode, the extent of impurity atoms in a tunnel diode

A)

is less

B)

is more

C)

is almost the same

D)

may be more or less

Correct Answer : is more

Explanation : Tunnel diode has heavily doped p and n regions.

232 .

In active filter circuits, inductances are avoided mainly because they

A)

saturate quickly

B)

are non-linear in nature

C)

are bulky and unsuitable for miniaturisation

D)

are always associated with some resistance

Correct Answer : are bulky and unsuitable for miniaturisation

Explanation : In active circuit, Inductors are used by Op-Amp resistors and capacitor instead of simple inductor.

233 .

When a p-n-p transistor is operating in active region, the current in the n region is due to

A)

mainly holes

B)

only holes

C)

only electrons

D)

mainly electrons

Correct Answer : mainly holes

Explanation : Since emitter is p-type, emitter current is mainly due to holes. This current diffuses through the base.

234 .

An extrinsic semiconductor sample has 6 billion silicon atoms and 3 million pentavalent impurity atoms. The number of electrons and holes is

A)

3 million each

B)

6 billion each

C)

3 million free electrons and very small number of holes

D)

3 million holes and very small number of free electrons

Correct Answer : 3 million free electrons and very small number of holes

Explanation : When pentavalent impurity is added, the number of fresh electrons is very large as compared to number of holes.

235 .

Photoconductive devices uses

A)

semiconductors

B)

metallic conductors

C)

good quality insulators

D)

Either (B) or (C)

Correct Answer : semiconductors

236 .

The early effect in a BJT is caused by

A)

fast turn on

B)

fast turn off

C)

large emitter base forward bias

D)

large collector base reverse bias

Correct Answer : large collector base reverse bias

237 .

In a common emitter BJT amplifier, the maximum usable supply voltage is limited by

A)

avalanche Beakdown of Base-Emitter junction

B)

zener break down voltage of the emitter base junction

C)

collector emitter breakdown voltage with base open(βV_CEO)

D)

collector emitter breakdown voltage with emitter open(βV_CEO)

Correct Answer : collector emitter breakdown voltage with emitter open(βV_CEO)

238 .

The temperature of cathode is increased from 2500K to 2600K. The increase in thermionic emission current is about

A)

0.1%

B)

4%

C)

50%

D)

150%

Correct Answer : 150%

239 .

E_g is the band gap, A is pre-factor, k is Boltzmann constant? Which one of the following is the remaining grade of paper used in paper capacitor, besides the other two grade of paper-low and extra low loss?

A)

Rough

B)

Regular

C)

High loss

D)

Strong dielectric

Correct Answer : Regular

240 .

Barkhausen criterion of oscillation is

A)

Aβ = 1

B)

Aβ > 1

C)

Aβ ≤ 1

D)

Aβ = < 1

Correct Answer : Aβ = 1

241 .

During induction heating of metals which of the following is abnormally high?

A)

Voltage

B)

Current

C)

Frequency

D)

Power factor

Correct Answer : Frequency

242 .

The output v-i characteristics of enhancement type MOSFET has

A)

only an ohmic region

B)

an ohmic region at low voltage value and a saturation region at high voltage

C)

only a saturation region

D)

a saturation region at low voltage value and an ohmic region at high voltage

Correct Answer : an ohmic region at low voltage value and a saturation region at high voltage

243 .

In a full wave rectifier, the current in each of the diodes flows for

A)

half cycle of the input signal

B)

one-fourth cycle of the input signal

C)

the complete cycle of the input signal

D)

less than half cycle of the input signal

Correct Answer : half cycle of the input signal

244 .

The rating of a transformer to deliver 100 watts of D.C. power to a load under half wave rectifier will be nearly

A)

1 kVA

B)

108 VA

C)

175 VA

D)

350 VA

Correct Answer : 350 VA

245 .

Which rectifier has the best ratio of rectification?

A)

Bridge rectifier

B)

Full wave rectifier

C)

Half wave rectifier

D)

Three phase full wave rectifier

Correct Answer : Three phase full wave rectifier

246 .

Which of the following are voltage controlled devices?

A)

Vacum triode

B)

FET

C)

SCR

D)

Both (A) and (B)

Correct Answer : Both (A) and (B)

247 .

Which impurity atom will give p type semiconductor when added to intrinsic semiconductor?

A)

Arsenic

B)

Boron

C)

Antimony

D)

Phosphorus

Correct Answer : Boron

248 .

Zener breakdown occurs

A)

in lightly doped junctions

B)

mostly in germanium junctions

C)

due to rapture of covalent band

D)

due to thermally generated minority carriers

Correct Answer : due to rapture of covalent band

249 .

The maximum power handling capacity of a resistor depends on

A)

resistance value

B)

total surface area

C)

thermal capacity of the resistor

D)

resistivity of the material used in the resistor

Correct Answer : thermal capacity of the resistor

250 .

In which mode of BJT operation are both junctions forward biased?

A)

Saturation

B)

Active

C)

Cut off

D)

Reverse active

Correct Answer : Saturation

251 .

Addition of a small amount of antimony to germanium will result in

A)

increased resistance

B)

formation of P-type semiconductor

C)

more free electrons than holes in the semiconductor

D)

antimony concentrating on the edges of the crystals

Correct Answer : more free electrons than holes in the semiconductor

252 .

A P-N junction offers

A)

conducts in reverse direction only

B)

conducts in forward direction only

C)

low resistance in forward as well as reverse direction

D)

high resistance in forward as well as reverse direction

Correct Answer : conducts in forward direction only

253 .

In modern MOSFETS, the material used for the gate is

A)

high purity silica

B)

high purity silicon

C)

epitaxial grown silicon

D)

heavily doped polycrystalline silicon

Correct Answer : heavily doped polycrystalline silicon

254 .

In a p-n-p transistor operating in forward active mode

A)

base is positive with respect to emitter and collector

B)

base is negative with respect to emitter and collector

C)

emitter is negative with respect to base and base is positive with respect to collector

D)

emitter is positive with respect to base and base is positive with respect to collector

Correct Answer : emitter is positive with respect to base and base is positive with respect to collector

255 .

If both the emitter base and the collector base junctions of a bipolar transistor are forward biased, the transistor is in the

A)

saturated region

B)

active region

C)

cut off region

D)

inverse mode

Correct Answer : saturated region

256 .

A varactor diode is

A)

unbiased

B)

forward biased

C)

reverse biased

D)

biased to breakdown

Correct Answer : reverse biased

257 .

In a triode the potential of grid (with respect to cathode) is usually

A)

zero

B)

negative

C)

positive

D)

zero or positive

Correct Answer : negative

258 .

In a photo transistor the photocurrent is

A)

collector

B)

emitter base junction

C)

collector base junction

D)

None of the above

Correct Answer : collector base junction

259 .

Hall effect is observed in a specimen when it is carrying current and is placed in a magnetic field. The resulting electric field inside the speciment will be in

A)

the direction of current

B)

direction antiparallel to magnetic field

C)

an arbitrary direction depend upon conductivity

D)

direction normal to both current and magnetic field

Correct Answer : direction normal to both current and magnetic field

260 .

In P-N junction, the region containing the uncompensated acceptor and donor ions is called

A)

depletion region

B)

active region

C)

neutral region

D)

transition zone

Correct Answer : depletion region

261 .

In a photodiode the current is due to

A)

majority carriers

B)

minority carriers

C)

both majority and minority carriers

D)

Either (A) or (C)

Correct Answer : minority carriers

262 .

If the temperature of on extrinsic semiconductor is increased so that the intrinsic carrier concentration is doubled, then

A)

the majority carrier density doubles

B)

the minority carrier density doubles

C)

both majority and minority carrier densities double

D)

the minority carrier density becomes 4 times the original value

Correct Answer : both majority and minority carrier densities double

263 .

At any point on the v-i characteristics of a semiconductor diode, the slope of v-i characteristics is called

A)

resistance of diode

B)

conductance of diode

C)

incremental resistance of diode

D)

incremental conductance of diode

Correct Answer : incremental conductance of diode

264 .

Which of the following statement about the photo electric emission is incorrect?

A)

The maximum velocity of emission varies with the intensity of light

B)

The maximum velocity of emission varies with the frequency of incident light

C)

The quantum yield depends on the frequency and not the intensity of incident light

D)

The amount of photoelectric emission is directly proportional to the intensity of light

Correct Answer : The maximum velocity of emission varies with the intensity of light

265 .

In a semiconductor avalanche breakdown occurs when

A)

potential barrier is reduced to zero

B)

reverse bias exceeds the limiting value

C)

forward bias exceeds the limiting value

D)

forward current exceeds the limiting value

Correct Answer : reverse bias exceeds the limiting value

266 .

No load d.c. output will be least in case of

A)

bridge rectifier

B)

half wave rectifier

C)

full wave rectifier

D)

three phase full wave rectifier

Correct Answer : half wave rectifier

267 .

When an electron breaks a covalent bond and moves away,

A)

a proton is also lost

B)

atom becomes an ion

C)

a hole is created

D)

rest of the electron move at a faster rate

Correct Answer : a hole is created

268 .

Germanium and Si phosphorus have their maximum spectral response in the

A)

X-ray region

B)

visible region

C)

infrared region

D)

ultraviolet region

Correct Answer : ultraviolet region

269 .

In which condition does BJT behave like a closed switch?

A)

Saturation

B)

Cut off

C)

Reverse active

D)

Forward active

Correct Answer : Saturation

270 .

High purity copper is obtained by

A)

casting

B)

rolling casting

C)

induction heating

D)

electrolytic refining

Correct Answer : electrolytic refining

271 .

In a JFET the width of channel is controlled by

A)

drain current

B)

gate voltage

C)

source current

D)

All of the above

Correct Answer : gate voltage

272 .

Figure represents a

A)

LED

B)

Varactor

C)

Zener diode

D)

Temperature dependent diode

Correct Answer : Zener diode

273 .

For generating 1 MHz frequency signal, the most suitable circuit is

A)

clapp oscillator

B)

colpitt's oscillator

C)

phase shift oscillator

D)

weinbridge oscillator

Correct Answer : colpitt's oscillator

274 .

A doped semi-conductor is called

A)

dipole semi-conductor

B)

impure semi-conductor

C)

extrinsic semi-conductor

D)

bipolar semi-conductor

Correct Answer : extrinsic semi-conductor

275 .

The first and the last critical frequency of an RC driving point impedance function must respectively by

A)

a zero and a pole

B)

a zero and a zero

C)

a pole and a pole

D)

a pole and a zero

Correct Answer : a zero and a pole

276 .

The diffusion current is proportional to

A)

applied electric field

B)

square of the electric field

C)

cube of the applied electric field

D)

concentration gradient of charge carrier

Correct Answer : concentration gradient of charge carrier

277 .

Which quantity controls the effectiveness of LED in emitting light?

A)

Temperature

B)

Current

C)

Applied voltage

D)

Extent of doping

Correct Answer : Temperature

278 .

Ferromagnetic materials exhibit

A)

a linear B-H behaviour

B)

a non-linear B-H behaviour

C)

an exponential B-H behaviour

D)

None of the above

Correct Answer : a non-linear B-H behaviour

279 .

The saturation current in a semi-conductor diode

A)

depends on reverse voltage

B)

depends on forward voltage

C)

is due to thermally generated minority carriers

D)

None of the above

Correct Answer : is due to thermally generated minority carriers

280 .

When a ferromagnetic substance is magnetised, there are small changes in its dimensions. This phenomenon is called

A)

hysteresis

B)

diamagnetism

C)

magnetostriction

D)

bipolar relaxation

Correct Answer : magnetostriction

281 .

Gold is often diffused into silicon PN junction devices to

A)

make silicon semimetal

B)

reduce the recombination rate

C)

increase the recombination rate

D)

make silicon a direct gap semiconductor

Correct Answer : make silicon a direct gap semiconductor

282 .

In the figure shows the circuits symbol of

A)

FET

B)

NMOSFET

C)

PMOSFET

D)

CMOSFET

Correct Answer : NMOSFET

283 .

Ferrites are

A)

ferromagnetic materials

B)

ferroelectric materials

C)

ferrimagnetic materials

D)

ferri-ferromagnetic materials

Correct Answer : ferromagnetic materials

284 .

In a p-n-p transistor the main current carriers and the mechanism of flow respectively are

A)

holes, drift

B)

holes, diffusion

C)

electrons, drift

D)

electrons, diffusion

Correct Answer : holes, diffusion

285 .

Secondary emission occurs in

A)

diode

B)

triode

C)

tetrode

D)

pentode

Correct Answer : tetrode

286 .

In fabricating silicon BJT in ICs by the epitaxial process, the number of diffusions used is usually

A)

2

B)

3

C)

4

D)

6

Correct Answer : 6

287 .

In a photo emissive device and emission efficiency is increased by

A)

cooling the anode

B)

heating the cathode

C)

coating the cathode ray by an active materials

D)

coating the cathode by an insulating material

Correct Answer : coating the cathode ray by an active materials

288 .

Materials in order of decreasing electrical conductivity are

A)

silver, copper, gold, aluminium

B)

gold, silver, copper, aluminium

C)

copper, silver, gold, aluminium

D)

aluminium, silver, gold, copper

Correct Answer : silver, copper, gold, aluminium

289 .

Which of the following exhibits negative resistance in a portion of its characteristics?

A)

JFET

B)

Tunnel diode

C)

Zener diode

D)

MOSFET and tunnel diode

Correct Answer : Tunnel diode

290 .

The emission of light is LED due to

A)

emission of holes

B)

emission of electrons

C)

conversion of heat energy into illumination

D)

generation of electromagnetic radiations

Correct Answer : generation of electromagnetic radiations

291 .

Which of the following is used as a passive component in electronic circuits?

A)

Capacitor

B)

Transistor

C)

Vacuum tube

D)

Tunnel diode

Correct Answer : Capacitor

292 .

The sum of two or more arbitrary sinusoidal is

A)

always periodic

B)

never periodic

C)

periodic under certain conditions

D)

periodic only if all the sinusoidals are identical in frequency and phase

Correct Answer : periodic only if all the sinusoidals are identical in frequency and phase

293 .

Peak inverse voltage will be highest for

A)

bridge rectifier

B)

full wave rectifier

C)

half wave rectifier

D)

three phase full wave rectifier

Correct Answer : full wave rectifier

294 .

Resistivity of metals is expressed in terms of

A)

Î¼ ohm-cm

B)

Î¼ ohm

C)

Î¼ ohm/cm

D)

Î¼ ohm-cm/Â°C

Correct Answer : Î¼ ohm-cm

295 .

The relation between plate current and plate voltage of a vacuum diode is called

A)

Ohm's law

B)

Boltzmann's law

C)

Langmuir Child law

D)

Richardson Dushman equation

Correct Answer : Langmuir Child law

296 .

The maximum rectification efficiency in case of full wave rectifier is

A)

40.6%

B)

66.6%

C)

81.2%

D)

100%

Correct Answer : 81.2%

297 .

For a full wave bridge rectifier supplied with 50 Hz a.c., the lowest ripple frequency will be

A)

50 Hz

B)

100 Hz

C)

200 Hz

D)

400 Hz

Correct Answer : 100 Hz

298 .

If 1 kVA transformer is used for all of the following rectifiers, the d.c. power availability will be least in case of

A)

bridge rectifier

B)

full wave rectifier

C)

half wave rectifier

D)

three phase full wave rectifier

Correct Answer : three phase full wave rectifier

299 .

Which of the following is the ferric electric material?

A)

Rochelle salt

B)

Barium titanate

C)

Potassium dihydrogen phosphate

D)

All of the above

Correct Answer : All of the above

300 .

The amount of time between the creation and disappearance of a hole in an intrinsic semiconductor material is called

A)

life time

B)

half life

C)

life cycle

D)

recombination time

Correct Answer : life time

301 .

In a N-type semi-conductor, the concentration of minority carriers is mainly depends on

A)

the extent of doping

B)

the number of donor atoms

C)

the temperature of the material

D)

the number of acceptor atoms

Correct Answer : the temperature of the material

302 .

The band gap of Si at room temperature is

A)

0.7 eV

B)

1.1 eV

C)

1.3 eV

D)

1.4 eV

Correct Answer : 1.1 eV

303 .

Transition capacitance is associated with __________ and depletion capacitance is associated with __________ diodes.

A)

reverse bias and forward bias

B)

reverse bias and reverse bias

C)

forward bias and reverse bias

D)

forward bias and forward bias

Correct Answer : reverse bias and reverse bias

304 .

If the energy gap of a semiconductor is 1.1 eV, then it would be.

A)

transparent to the visible light

B)

opaque to the infrared radiation

C)

transparent to the ultraviolet radiation

D)

opaque to the visible light

Correct Answer : opaque to the visible light

305 .

The primary reason for the widespread use of Si in semiconductor device technology is

A)

lower melting point

B)

abundance of Si on the surface of earth

C)

larger band gap of Si in comparison to Ge

D)

favourable properties of Silicon-dioxide (SiOâ‚‚)

Correct Answer : favourable properties of Silicon-dioxide (SiOâ‚‚)

306 .

If the conductivity of pure germanium is 1.54 siemens/metre, its resistivity in ohm-metre will be nearly

A)

65

B)

6.5

C)

0.65

D)

0.065

Correct Answer : 6.5

307 .

Under low level injection assumption, the infected minority carrier current for an extrinsic semiconductor is essentially the

A)

drift current

B)

induced current

C)

diffusion current

D)

recombination current

Correct Answer : diffusion current

308 .

As the reverse voltage is increased, the depletion layer

A)

widens

B)

reduce to zero

C)

becomes narrow

D)

remains the same

Correct Answer : widens

309 .

If an electron move through a potential difference of 500 V, the energy possesses by it will be

A)

500 eV

B)

500 mV

C)

500 ergs

D)

500 joules

Correct Answer : 500 eV

310 .

In which of the following does a negative resistance region exist in the v-i characteristics?

A)

PIN diode

B)

Zener diode

C)

Schottky diode

D)

Tunnel diode

Correct Answer : Tunnel diode

311 .

The intrinsic resistivity of silicon at 300 K is about

A)

1 Î©-cm

B)

400 Î©-cm

C)

10000 Î©-cm

D)

230000 Î©-cm

312 .

What happens when forward bias is applied to a junction diode?

A)

Potential barrier is increased

B)

Potential barrier is decreased

C)

Majority carrier current is reduced to zero

D)

Minority carrier current is reduced to zero

Correct Answer : Potential barrier is decreased

313 .

A differential amplifier is invariably used in the I/P stage of all OP-amps. This is done basically to produce the OP-amp with a very high.

A)

CMRR

B)

slew rate

C)

bandwidth

D)

open-loop gain

Correct Answer : open-loop gain

314 .

The probability giving distribution of electrons over a range of allowed energy levels is known as

A)

Fermi-Dirac Distribution

B)

Maxwell's Distribution

C)

Richardson Dushman Distribution

D)

None of the above

Correct Answer : Fermi-Dirac Distribution

315 .

The resistivity of ferrites is

A)

slightly higher than that of the ferromagnetic metals

B)

slightly lower than that of the ferromagnetic materials

C)

very much higher than that of the ferromagnetic metals

D)

very much lower than that of the ferromagnetic metals

Correct Answer : very much higher than that of the ferromagnetic metals

316 .

In monostable multivibrator

A)

has no stable state

B)

has one stable state

C)

has two stable states

D)

switches automatically from one state to other state

Correct Answer : has one stable state

317 .

In which of the following case the rating of the transformer to deliver 100 watts of d.c. power to a load, will be least?

A)

Half wave rectifier

B)

Full wave rectifier

C)

Bridge type full wave rectifier

D)

Three phase full wave rectifier

Correct Answer : Three phase full wave rectifier

318 .

A potential difference is developed across a current carrying metal strip when the strip is placed in a transverse magnetic field. The above effect is known as

A)

Fermi's effect

B)

Hall's effect

C)

Joule's effect

D)

Photo electric effect

Correct Answer : Hall's effect

319 .

The maximum forward current in case of signal diode is in the range of

A)

few milli amperes

B)

1 A to 10 A

C)

0.1 A to 1 A

D)

few nano amperes

Correct Answer : few milli amperes

320 .

On which of the following effect do thermocouples work?

A)

Joule effect

B)

Peltier effect

C)

Seeback effect

D)

Thomson effect

Correct Answer : Seeback effect

321 .

Resistivity of carbon is around

A)

10 to 70 m-ohm-cm

B)

80 to 130 m-ohm-cm

C)

800 to 1300 m-ohm-cm

D)

8000 to 13000 m-ohm-cm

Correct Answer : 800 to 1300 m-ohm-cm

322 .

Which of the following is anti-ferromagnetic material?

A)

NIO

B)

CrSb

C)

MnO

D)

All of the above

Correct Answer : All of the above

323 .

Almost all resistors are made in a monolithic integrated circuit

A)

during the base diffusion

B)

during the entire diffusion

C)

during the collector diffusion

D)

while growing the epitaxial layer

Correct Answer : during the entire diffusion

324 .

For an n-channel JEFT having drain source voltage constant if the gate source voltage is increased (more negative) pinch off would occur for

A)

zero drain current

B)

high values of drain current

C)

saturation values of drain current

D)

gate current equal to the drain current

Correct Answer : zero drain current

325 .

The capacitor filter provides poor voltage regulation because

A)

filter promotes ripple at peak voltage

B)

the increase in ripple with load current causes a increase in average voltage

C)

the increase in ripple with load current causes a decrease in average voltage

D)

None of the above

Correct Answer : the increase in ripple with load current causes a decrease in average voltage

326 .

In the schematic representation of bipolar junction transistor, the direction of arrow shows the direction of flow of

A)

holes

B)

electrons

C)

holes in pnp and electrons in npn

D)

electrons in pnp and holes in npn

Correct Answer : holes

327 .

The forbidden band in semiconductors is of the order of

A)

0.01 eV

B)

1 eV

C)

6 eV

D)

10 eV

Correct Answer : 1 eV

328 .

For an P-N-P transistor in normal operation its junction are biased as

A)

emitter base : reverse, collector base : reverse

B)

emitter base : reverse, collector base : forward

C)

emitter base : forward, collector base : forward

D)

emitter base : forward, collector base : reverse

Correct Answer : emitter base : forward, collector base : reverse

329 .

For radiating ultraviolet rays, LEDs use

A)

gallium arsenide

B)

zinc sulphide

C)

gallium phosphide

D)

None of the above

Correct Answer : zinc sulphide

330 .

The kinetic energy of photoelectrons emitted by a photo sensitive surface depends on

A)

angle of incidence of radiation

B)

surface conditions of the surface

C)

intensity of the incident radiation

D)

wavelength of the incident radiation

Correct Answer : wavelength of the incident radiation