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ECE : Materials and Components - Quiz(MCQ)
1 .
On the basis of the type of chemical bonds, solids may be classified into
A)
Ionic crystals
B)
Ionic and valence crystals
C)
Ionic crystal, valence crystals and metals
D)
Ionic crystals, valence crystals, metal and vander wall crystals

Correct Answer :   Ionic crystals, valence crystals, metal and vander wall crystals

2 .
In an intrinsic semiconductor, at a given temperature T
A)
The number of electrons-hole pairs generated per second due to thermal motion are equal to the number of electron-hole pairs lost per second due to recombination
B)
The number of electron-hole pairs generated per second due to thermal motion is always less than the number of electron-hole pairs lost per second due to recombination
C)
The number of electron hole pairs generated per second due to thermal motion is always more than the number of electron-hole pairs lost per second due to recombination
D)
All of the above

Correct Answer :   The number of electrons-hole pairs generated per second due to thermal motion are equal to the number of electron-hole pairs lost per second due to recombination

3 .
Which capacitor-store higher amount of energy?
A)
Air capacitor
B)
Mica capacitor
C)
Paper capacitor
D)
Plastic film capacitor

Correct Answer :   Mica capacitor

Explanation : Energy stored is proportional to capacitance and capacitance is proportional to permittivity.

4 .
In paramagnetic materials
A)
permanent magnetic dipole do not exist
B)
permanent magnetic dipoles exist but the interaction between neighbouring dipoles is negligible
C)
permanent magnetic dipole moment may or may not exist
D)
permanent magnetic dipoles exist and the interaction between neighbouring dipoles is very strong

Correct Answer :   permanent magnetic dipoles exist but the interaction between neighbouring dipoles is negligible

Explanation : In paramagnetic materials interaction between neighbouring dipoles is negligible.

5 .
The temperature below which certain materials are antiferromagnetic and above which they are paramagnetic is called
A)
Curie temperature
B)
Weiss temperature
C)
Neel temperature
D)
None of the above

Correct Answer :   Neel temperature

6 .
Ferrites have
A)
low eddy current loss
B)
low resistivity
C)
a low copper loss
D)
higher specific gravity compared to iron

Correct Answer :   low eddy current loss

Explanation : Resistivity of ferrites is very high as compared to that of iron. Hence eddy curretns are much less.

7 .
For making a capacitor it is better to have a dielectric having
A)
Low permittivity
B)
Permittivity same as that of air
C)
High permittivity
D)
Permittivity which is neither high nor low

Correct Answer :   High permittivity

8 .
Which inductor is linear?
A)
Air cored
B)
Cast iron cored
C)
Iron alloy cored
D)
Sheet steel cored

Correct Answer :   Air cored

9 .
As the viscosity of a liquid increases, the relaxation time
A)
Increases
B)
Decreases
C)
Remains constant
D)
First decreases then increases

Correct Answer :   Increases

10 .
Debye temperature of metals is
A)
About 10 K
B)
About 200 K
C)
About 600 K
D)
About 80 K

Correct Answer :   About 200 K

11 .
Schrodinger wave equation is a
A)
Linear equation
B)
Differential equation
C)
Partial differential equation
D)
None of the above

Correct Answer :   Partial differential equation

12 .
At room temperature the number of conducting electrons in an intrinsic semiconductor
A)
Is about half the number of valence electrons
B)
Is almost equal to the number of valence electrons
C)
Is small as compared to the number of valence electrons
D)
Is a very small fraction of the number of valence electrons

Correct Answer :   Is a very small fraction of the number of valence electrons

13 .
In solid insulator materials having only one kind of atom, the types of polarization which exist are
A)
Electronic only
B)
Electronic and ionic
C)
Electronic and permanent
D)
Electronic, ionic and permanent

Correct Answer :   Electronic only

14 .
Which of the following are true for relative dielectric constant?

1. It is dimensionless.
2. It is equal to 1 for vacuum.
3. It is equal to 1 for all substances.
A)
1 and 2 only
B)
2 and 3 only
C)
1 and 3 only
D)
1, 2 and 3

Correct Answer :   1 and 2 only

15 .
When a material becomes a superconductor, its resistivity becomes
A)
zero
B)
very small
C)
about 10% of normal value
D)
about 20% of normal value

Correct Answer :   zero

16 .
In a piezoelectric crystal, the application of mechanical force will cause
A)
shift in Fermi level
B)
plastic deformation of crystal
C)
magnetic dipoles in the crystal
D)
electrical polarization in the crystal

Correct Answer :   magnetic dipoles in the crystal

Explanation : Piezoelectric materials permit conversion of mechanical force into electrical energy.

17 .
As the temperature of a pure silicon specimen is increased
A)
the number of holes increases
B)
the number of holes decreases
C)
the number of free electrons increases
D)
the number of free electrons and holes increases

Correct Answer :   the number of free electrons and holes increases

18 .
At a very low temperature, a semiconductor
A)
becomes a conductor
B)
becomes an insulator
C)
may become a conductor or an insulator
D)
will remain a semiconductor becomes a conductor or an insulator

Correct Answer :   becomes an insulator

19 .
The colour code on a carbon resistor is red-red-black-silver. The value of resistor is
A)
2200 Ω
B)
22 ± 10% Ω
C)
22000 Ω
D)
22 ± 5% Ω

Correct Answer :   22 ± 10% Ω

20 .
Some typical examples of macroscopic quantities are
A)
µr
B)
conductivity
C)
dielectric constant
D)
All of the above

Correct Answer :   All of the above

21 .
The resistance of a photoconductor
A)
Decreases with increase in light intensity
B)
Remains constant
C)
Increases with increase in light intensity
D)
May increase or decrease with increase in light intensity

Correct Answer :   Decreases with increase in light intensity

22 .
Electrical contact materials used in switches, brushes, relay must possess
A)
High thermal conductivity and low melting point
B)
Low thermal conductivity and low melting point
C)
High thermal conductivity and high melting point
D)
Low thermal conductivity and high melting point

Correct Answer :   High thermal conductivity and high melting point

23 .
Which inductor is used at high frequencies?
A)
Ceramic cored
B)
Cast iron cored
C)
Iron alloy cored
D)
Sheet steel cored

Correct Answer :   Ceramic cored

24 .
The dielectric losses do not depend on frequency.
A)
True
B)
False
C)
Can Not Say
D)
None of the above

Correct Answer :   False

25 .
An atom of a rare gas is placed is an electric field E. Then
A)
The nucleus will not be shifted.
B)
The nucleus will be shifted in a direction opposite to that of E.
C)
The nucleus will be shifted in the direction of E by an amount which is independent of E.
D)
The nucleus will be shifted in the direction of E by an amount which is proportional to E.

Correct Answer :   The nucleus will be shifted in the direction of E by an amount which is proportional to E.

26 .
Above a certain temperature, the specific heat of a metal becomes constant. This temperature is called
A)
Neel temperature
B)
Debye temperature
C)
Curie temperature
D)
Transition temperature

Correct Answer :   Debye temperature

27 .
The rule that resistivity of conductors can be separated into two parts viz. temperature independent and temperature dependent is known as
A)
Debye rule
B)
Curie rule
C)
Matthiessen’s rule
D)
Onne’s rule

Correct Answer :   Matthiessen’s rule

28 .
As the atoms of rare gases become larger, electronic polarizability
A)
Increases
B)
Decreases
C)
Remains the same
D)
May increase or decrease

Correct Answer :   Remains the same

29 .
When a material is in superconducting state and a magnetic field is applied
A)
The superconducting property may be destroyed
B)
The material may become an insulator
C)
The superconducting property is not affected
D)
The superconducting property may be affected and resistivity may increase from zero to a low value

Correct Answer :   The superconducting property may be destroyed

30 .
The unit for mmf is
A)
A
B)
Wb
C)
T
D)
V

Correct Answer :   A

31 .
The phenomenon of dielectric hysteresis occurs with
A)
DC
B)
AC
C)
Both AC and DC
D)
None of the above

Correct Answer :   AC

32 .
Hall effect is observed in a specimen (metal or semi conductor) when it is carrying current and is placed in a magnetic field. The resultant electric field inside the specimen is
A)
In the same direction as current
B)
In a direction anti parallel to magnetic field
C)
Both (A) and (B)
D)
Normal to both current and magnetic field

Correct Answer :   Normal to both current and magnetic field

33 .
Semi conducting materials are all
A)
elements
B)
compounds
C)
elements or mixtures
D)
elements or compounds

Correct Answer :   elements or compounds

34 .
Silicon and germanium atoms combine orderly into array of atoms located in repetitive geometric pattern. This pattern is called
A)
crystal
B)
molecule
C)
valence bond
D)
covalent bond

Correct Answer :   crystal

35 .
In a pure sample of silicon
A)
the number of free electrons is less than number of holes
B)
the number of free electrons is more than the number of holes
C)
the number of holes and free electrons is always equal
D)
the number of free electrons and holes is equal at low temperature

Correct Answer :   the number of holes and free electrons is always equal

36 .
In a homogeneous magnetic field H of a solenoid, the core carries a magnetic dipole moment M per unit volume equal to
A)
μ0 H
B)
μr H
C)
μoμr H
D)
(μr - 1) H

Correct Answer :   (μr - 1) H

37 .
Assertion (A) : Silicon is the most favoured semiconductor material.

Reason (R) : PIV for silicon diode is more than that for germanium diode.
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 correct explanation of A

Correct Answer :   A is true but R is false

38 .
Resistivity of rubber is about
A)
10² Ω-m
B)
10⁻² Ω-m
C)
5 x 10⁸ Ω m
D)
5 x 10¹² Ω-m

Correct Answer :   5 x 10¹² Ω-m

39 .
An iron specimen has µr = 1000 when B = 0.3 T. If B = 0.35 T, µr
A)
will be 1000
B)
will be less than 1000
C)
will be more than 1000
D)
may be more or less than 1000

Correct Answer :   may be more or less than 1000

40 .
The colour code on a carbon resistor is green-blue-yellow. The tolerance is
A)
± 5%
B)
± 10%
C)
± 20%
D)
± 30%

Correct Answer :   ± 20%

41 .
Permeability is analogous to
A)
resistivity
B)
conductivity
C)
coercivity
D)
retentivity

Correct Answer :   conductivity

42 .
The resistivity of intrinsic semiconductors, at room temperature, is of the order of
A)
1 Ω-m
B)
1000 Ω-m
C)
10⁶ Ω-m
D)
10⁻³ Ω-m

Correct Answer :   1 Ω-m

43 .
In terms of classical representation of electrons
A)
an atom is essentially full
B)
an atom is essentially empty
C)
an atom may be essentially empty or full depending on the material
D)
an atom may be essentially empty or full depending on temperature

Correct Answer :   an atom is essentially empty

44 .
The merger of hole and free electron is called
A)
Free electrons
B)
Thermal energy
C)
Covalent bonding
D)
Recombination

Correct Answer :   Recombination

45 .
In a metal, the valence electrons
A)
Are not shared
B)
Are shared only between neighbouring atoms
C)
Are shared by all atoms
D)
Either (B) or (C)

Correct Answer :   Are shared by all atoms

46 .
The number of protons in a copper atom are
A)
2
B)
9
C)
11
D)
29

Correct Answer :   29

47 .
With increase in temperature, the electrical conductivity would
A)
Decrease in metals but increase in intrinsic semiconductor
B)
Increase in metals as well as in intrinsic semiconductor
C)
Decrease in metals as well as in intrinsic semiconductor
D)
Increase in metals but decrease in intrinsic semiconductor

Correct Answer :   Decrease in metals but increase in intrinsic semiconductor

48 .
The fact that domains exhibits spontaneous magnetisation is
A)
Curie-Weiss law
B)
Second hypothesis is of Weiss
C)
Boltzmann’s statistics
D)
First hypothesis is of Curie

Correct Answer :   Second hypothesis is of Weiss

49 .
If a small amount of Cu is added to Ni conductor, then
A)
Resistivity of Ni remains the same
B)
Resistivity of Ni will decrease at all temperatures because Cu is a better conductor than Ni
C)
Residual resistivity of Ni at low temperature will increase as Cu atoms act as defect centres
D)
Resistivity of Ni will increase at all temperatures as Cu destroys the periodicity of Ni and acts as defects

Correct Answer :   Resistivity of Ni will increase at all temperatures as Cu destroys the periodicity of Ni and acts as defects

50 .
Assertion (A) : Intrinsic resistivity of silicon is lower than that of germanium.

Reason (R) : Magnitude of free electron concentration in germanium is more than that of silicon.
A)
A is false but R is true
B)
A is true but R is false
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 correct explanation of A

Correct Answer :   A is false but R is true

51 .
A copper atom is neutral. Its core has a net charge of
A)
0
B)
+ 1
C)
-1
D)
+2

Correct Answer :   + 1

52 .
As the temperature of semiconductor is increased
A)
the average number of free charge carriers decreases
B)
the average number of free charge carriers remains the same
C)
the average number of free charge carriers increases
D)
the average number of free charge carriers may increase or decrease

Correct Answer :   the average number of free charge carriers increases

53 .
In anti-ferromagnetic materials, the graph of susceptibility versus temperature shows a sharp maximum at a certain temperature. This temperature is known as
A)
Bitter temperature
B)
Neel temperature
C)
Curie temperature
D)
Weiss temperature

Correct Answer :   Neel temperature

54 .
A piece of copper and another piece of Germanium are cooled from 30°C to 80 K. The resistance of
A)
both increases
B)
both decreases
C)
copper increases and germanium decreases
D)
copper decreases and germanium increases

Correct Answer :   copper decreases and germanium increases

Explanation : As temperature is decreased, resistance of conductors decreases and resistance of semiconductors increases.

55 .
The most important set of specifications of transformer oil include
A)
dielectric strength and viscosity
B)
viscosity and flash point
C)
flash point and viscosity
D)
dielectric strength and flash point

Correct Answer :   dielectric strength and viscosity

56 .
The residual resistivity of a binary alloy at 0 K is
A)
Product of residual resistivities of component metals
B)
Sum of residual resistivities of component metals
C)
Difference of residual resistivities of component metals
D)
Dependent on the concentration of minor component in the alloy

Correct Answer :   Dependent on the concentration of minor component in the alloy

57 .
The elements which become superconducting at extremely low temperatures are
A)
Ferromagnetic at room temperature
B)
Relatively poor conductors at room temperature
C)
Insulators at room temperature
D)
Good conductors at room temperature

Correct Answer :   Relatively poor conductors at room temperature

58 .
The number of protons in a silicon atom are
A)
4
B)
8
C)
12
D)
14

Correct Answer :   14

59 .
For dielectrics in alternating field, polarizability αe is a complex quantity. The imaginary part of αe is zero for
A)
ω = 0
B)
ω → ∞
C)
ω = 0 and ω → ∞
D)
ω = natural frequency ω0

Correct Answer :   ω = 0 and ω → ∞

Explanation : Imaginary part of αe is zero for ω = 0 and ω = ∞.

60 .
In the wave mechanical theory, the maximum of the charge distribution in the ground state occurs for a distance from the nucleus equal to
A)
first Bohr radius
B)
second Bohr radius
C)
third Bohr radius
D)
either first or second Bohr radius

Correct Answer :   first Bohr radius

Explanation : The total charge associated with an electron moving about nucleus in the ground state of hydrogen atom is given by  4π²rp(r)dr.

This integrand has a maximum value at r = radius of first Bohr orbit.

61 .
The temperature at which some materials become superconductors is called
A)
Neel temperature
B)
Transition temperature
C)
Curie temperature
D)
Onnes temperature

Correct Answer :   Transition temperature

62 .
In Fermi-Dirac statistics, the probability of electron occupation of an energy level equal to Fermi level is
A)
0
B)
0.25
C)
0.5
D)
1

Correct Answer :   0.5

63 .
The quantum numbers associated with electron motion are designed as
A)
a, b, c
B)
h, k, l
C)
h, n, l
D)
n, m, l

Correct Answer :   n, m, l

64 .
Which of these has lowest dielectric strength?
A)
Paper
B)
Dry air
C)
Cotton
D)
Wet air

Correct Answer :   Wet air

Explanation : Cotton and paper have higher dielectric strength than air. Moisture decreases dielectric strength.

65 .
As per Curie-Weiss law, the magnetic susceptibility of a material varies as
A)
1/T
B)
T
C)
T²
D)
T⁻²

Correct Answer :   1/T

66 .
The amount of time between the creation and recombination of a free electron and hole is called
A)
lorentz time
B)
life time
C)
collision time
D)
relaxation time

Correct Answer :   life time

67 .
For iron, the ferromagnetic Curie temperature is
A)
about 20 K
B)
about -20°C
C)
about 1000 K
D)
about 100°C

Correct Answer :   about 1000 K

68 .
As regards dielectric constant εr
A)
it is dimensionless
B)
the units are farads
C)
the units are farads/m
D)
the units are newton/coulomb

Correct Answer :   it is dimensionless

69 .
Resistivity of copper is lower than that of nickel. When a small percentage of copper is added to nickel, the resistivity
A)
increases
B)
decreases
C)
remains the same
D)
may increase or decrease

Correct Answer :   increases

70 .
The conductivity of intrinsic semiconductor is given by
A)
ni(μpμn)
B)
eni(μp + μn)
C)
ni(μp + μn)
D)
eni(μp - μn)

Correct Answer :   eni(μp + μn)

Explanation : Conductivity = (Electron charge) x (Number of charge carriers) x (Sum of mobilities of holes and electrons).

71 .
The core of a coil has a length of 10 cm. The self inductance is 8 mH. If the core length is doubled, all other quantities remaining the same, the self inductance will be
A)
4 mH
B)
8 mH
C)
16 mH
D)
32 mH

Correct Answer :   4 mH

72 .
The minority carrier life time and diffusion constant in a semiconducting material are 100 μs and 100 cm²/s respectively. The diffusion length of carriers is
A)
0.1 cm
B)
0.01 cm
C)
0.0141 cm
D)
1 cm

Correct Answer :   0.1 cm

Explaination : Diffusion length = sqrt(Carrier life time x Diffusion constant) = (100 x 10⁻⁶ x 100)⁰⋅⁵ = 0.1 cm.

73 .
Assertion (A) : Electronic and Ionic polarization in a polyatomic gas are independent of temperature.

Reason (R) : The orientation polarization is independent of temperature.
A)
A is false but R is true
B)
A is true but R is false
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 correct explanation of A

Correct Answer :   A is true but R is false

74 .
Two materials having temperature coefficients of 0.004 and 0.0004 respectively are joined in series. The overall temperature coefficient is likely to be
A)
0.04
B)
0.08
C)
0.001
D)
0.0001

Correct Answer :   0.001

75 .
The number of valence electrons in pentavalent impurity is
A)
1
B)
3
C)
4
D)
5

Correct Answer :   5

76 .
If the diameter of a wire is doubled, its current carrying capacity becomes
A)
half
B)
twice
C)
one-fourth
D)
four times

Correct Answer :   four times

77 .
The law J = σE, where J is current density, σ is electrical conductivity and E is field strength is
A)
Ohm's law
B)
Gauss law
C)
Ampere's law
D)
Biot-Savart law

Correct Answer :   Ohm's law

78 .
Material which lack permanent magnetic dipoles are known as
A)
ferrimagnetic
B)
diamagnetic
C)
paramagnetic
D)
ferromagnetic

Correct Answer :   diamagnetic

79 .
A parallel plate capacitor has its length, width and separation doubled. It fringing effects are neglected, to keep the capacitance same, the dielectric constant must be
A)
doubled
B)
kept the same
C)
halved
D)
made 4 times

Correct Answer :   halved

Explanation : C= ∈0∈A/d When dimensions are changed, A become four times and d becomes twice.

Since ∈0 is constant, ∈r must be halved to keep C constant.

80 .
If a sample of germanium and a sample of silicon have the same impurity density and are kept at room temperature
A)
both will have equal value of resistivity
B)
both will have equal negative resistivity
C)
resistivity of germanium will be higher than that of silicon
D)
resistivity of silicon will be higher than that of germanium

Correct Answer :   resistivity of silicon will be higher than that of germanium

81 .
For a photoconductor with equal electron and hole mobilities and perfect ohmic contacts at the ends, an increase in intensity of optical illumination results in
A)
increase in resistance
B)
decrease in resistance
C)
a change in s.c current
D)
a change in o.c voltage

Correct Answer :   decrease in resistance

Explaination : It is the characteristic of a photoconductor that its resistance decreases with increase in illumination.

82 .
A permeable substance is one
A)
which is strong magnet
B)
which is a weak magnet
C)
which is a good conductor
D)
through which magnetic lines of force can pass easily

Correct Answer :   through which magnetic lines of force can pass easily

83 .
The classes of solid dielectrics are
A)
A E B F H C
B)
Y A E B F H C
C)
A E B F H C D
D)
A, B, C, D, E, F, H

Correct Answer :   Y A E B F H C

84 .
A 200 turn coil has a self inductance of 10 mH. If the number of turns is doubled, all other quantities remaining the same, the self inductance will be
A)
40 mH
B)
20 mH
C)
5 mH
D)
2.5 mH

Correct Answer :   40 mH

85 .
A material which is lightly repelled by a magnetic field is known as
A)
non-magnetic material
B)
paramagnetic material
C)
diamagnetic material
D)
ferromagnetic material

Correct Answer :   diamagnetic material

86 .
Which of the following is the poorest conductor of electricity?
A)
Copper
B)
Nichrome
C)
Aluminium
D)
All of the above

Correct Answer :   Nichrome

87 .
The magnetic moment in units of Bohr magneton of a ferrous ion in any ferrite is
A)
0
B)
2
C)
4
D)
6

Correct Answer :   4

88 .
The relaxation time of electrons in a metal is of the order of
A)
10⁻⁶ secs
B)
10⁻¹⁰ secs
C)
10⁻¹⁴ secs
D)
10⁻²⁰ secs

Correct Answer :   10⁻¹⁴ secs

89 .
In a specimen of silicon steel, a field strength of 200 A/m causes a flux density of 0.5 T. In a specimen of cast iron, the same H would cause B to be
A)
0.5 T
B)
less than 0.5 T
C)
more than 0.5 T
D)
0.5 T or more or less

Correct Answer :   less than 0.5 T

90 .
A liquid has N permanent dipoles μp per unit volume and has been subjected to dc field for a long time such that orientation polarization is P0. At t = 0, the field is suddenly removed, then polarization
A)
will remain constant at P0
B)
will become zero at t = 0
C)
Either (A) or (B)
D)
will delay to zero with a time constant

Correct Answer :   will delay to zero with a time constant

91 .
Inductors used at V.H.F. are made using
A)
thin film technique
B)
air core
C)
cast iron cored
D)
sheet steel cored

Correct Answer :   thin film technique

92 .
Nichrome is used for
A)
lamp filaments
B)
heater coils
C)
overload line wires
D)
All of the above

Correct Answer :   heater coils

Explanation : Because heater coil must be made of high resistivity material.

93 .
If k is Boltzmann's constant and T is absolute temp, then at room temp.
A)
kT ≃ 1 eV
B)
kT ≃ 0.5 eV
C)
kT ≃ 100 eV
D)
kT ≃ 0.025 eV

Correct Answer :   kT ≃ 0.025 eV

94 .
If the valence electron is separated from a copper atom, the remaining part of atom has a net charge of
A)
1
B)
- 1
C)
0
D)
+3

Correct Answer :   1

95 .
For a core having a relative permeability μr, magnetic dipole moment per unit volume M and field strength H, the flux density B is
A)
B = μr (H + M)
B)
B = μ0 (H + M)
C)
B = μ0μr (H + M)
D)
B = μ0μr (H - M)

Correct Answer :   B = μ0 (H + M)

96 .
In which of the following semiconductor are holes majority carriers
A)
intrinsic
B)
extrinsic
C)
p type
D)
n type

Correct Answer :   p type

97 .
When a ferromagnetic substance is magnetised there are small changes in dimensions. This phenomenon is called
A)
hysteresis
B)
magnetostriction
C)
diamagnetism
D)
dipolar relaxation

Correct Answer :   magnetostriction

98 .
An electron in a homogeneous magnetic field and having velocity perpendicular to the direction of field moves
A)
along the field
B)
perpendicular to the field
C)
in a circular path
D)
along a straight line inclined at 45° to field

Correct Answer :   in a circular path

99 .
For a given value (n) of principle quantum number, the number of possible electronic states are
A)
n
B)
n²
C)
n³
D)
√n

Correct Answer :   n²

Explanation : The total number of states corresponding to a given value of n is equal to


(2l + 1) = 1 + 3 + .... + [2(n-1) + 1] = n².

100 .
Electrical conductivity of metals expressed in ohm⁻¹ m⁻¹ is of the order of
A)
10⁵
B)
10¹⁰
C)
10⁻⁴
D)
10⁻⁶

Correct Answer :   10⁵

Explanation : Conductivity is reciprocal of resistivity. Since resistivity of metals is around 10⁻⁷ ohm-m, conductivity is about 10⁷ ohm⁻¹ m⁻¹. So 10⁵ is the nearest value.

101 .
In a metal the probability of a state 0.1 eV below Fermi level being occupied
A)
is less than the probability of state 0.1 eV above Fermi level being occupied
B)
is the same as the probability of state 0.1 eV above Fermi level being occupied
C)
may be equal to or more or less than the probability of state 0.1 eV above Fermi level being occupied
D)
is more than the probability of state 0.1 eV above Fermi level being occupied

Correct Answer :   is more than the probability of state 0.1 eV above Fermi level being occupied

102 .
A dielectric is subjected to alternating field. The dielectric losses are potential to
A)
real part of dielectric constant
B)
either real or imaginary part of dielectric constant
C)
imaginary part of dielectric constant
D)
both real and imaginary parts of dielectric constant

Correct Answer :   imaginary part of dielectric constant

Explanation : Absorption of energy is proportional to imaginary part of complex dielectric constant.

103 .
In anti-ferromagnetic materials, the graph of susceptibility versus temperature shows a sharp maximum at a certain temperature. This temperature is known as
A)
Curie temperature
B)
Neel temperature
C)
Weiss temperature
D)
Bitter temperature

Correct Answer :   Neel temperature

104 .
The wavelength of light emitted by GaAs laser is 8670 x 10⁻¹â° m. If h = 6.626 x 10⁻³â´ Js, velocity of light = 3 x 10⁸ m/s and eV = 1.602 x 10⁻¹â¹ J, the energy gap in GaAs is
A)
0.18 eV
B)
0.7 eV
C)
1.43 eV
D)
2.39 eV

Correct Answer :   1.43 eV

105 .
The direction of force an a conductor carrying current and lying in a magnetic field can be found by using
A)
Cork screw rule
B)
Fleming's right hand rule
C)
Fleming's left hand rule
D)
All of the above

Correct Answer :   Fleming's left hand rule

106 .
The units for electric dipole moment are
A)
coulombs
B)
colomb-metre
C)
coulomb/metre
D)
coulomb/m²

Correct Answer :   colomb-metre

107 .
The temperature coefficient of resistivity of semiconductors is
A)
negative
B)
positive
C)
may be positive or negative
D)
None of the above

Correct Answer :   negative

108 .
Which of the following is used in automatic control of street lights?
A)
Varistor
B)
Transistor
C)
Thermistor
D)
Photoconductor

Correct Answer :   Photoconductor

109 .
The current flow in a semiconductor is due to
A)
holes
B)
electrons
C)
holes and electrons
D)
holes, electrons and ions

Correct Answer :   holes and electrons

110 .
Eddy current loss is
A)
proportional to frequency
B)
independent of frequency
C)
proportional to (frequency)²
D)
proportional to (frequency)³

Correct Answer :   proportional to (frequency)²

111 .
A good dielectric should have
A)
low losses
B)
high intrinsic strength
C)
good heat conductivity
D)
All of the above

Correct Answer :   All of the above

112 .
The number of protons in germanium atom is
A)
32
B)
28
C)
16
D)
4

Correct Answer :   32

113 .
Sulphur hexafluoride is used in
A)
relays
B)
generators
C)
circuit breakers
D)
transformers

Correct Answer :   circuit breakers

Explanation : Sulphur hexafluoride is used in circuit breakers for arc quenching and insulation.

114 .
The number of valence electrons in trivalent impurity is
A)
1
B)
3
C)
4
D)
5

Correct Answer :   3

115 .
A capacitor can be represented by a capacitance and resistance in parallel. For a good capacitor, this parallel resistance should be
A)
low
B)
high
C)
negligible
D)
very high

Correct Answer :   very high

116 .
The colour code on a carbon resistor is brown-black-red-gold. The value of resistance is
A)
100 Ω
B)
1000 Ω
C)
1000 Ω ± 5%
D)
1000 Ω ± 10%

Correct Answer :   1000 Ω ± 5%

117 .
If the operating temperature increases by 10°C, the rate of deterioration of solid dielectric becomes
A)
one and a half time
B)
double
C)
3 times
D)
4 times

Correct Answer :   double

118 .
In which of the following semiconductor are holes minority carriers
A)
n type
B)
p type
C)
extrinsic
D)
intrinsic

Correct Answer :   n type

119 .
The Ohm's law for conduction in metals is
A)
J = σE
B)
J = E/σ
C)
J ∝ σE
D)
J ∝ E/S

Correct Answer :   J = σE

120 .
The measurement of Hall coefficient of a semiconductor with one type of charge carriers gives the information about
A)
sign of charge carrier
B)
density of charge carrier
C)
both sign and density of charge carrier
D)
None of the above

Correct Answer :   both sign and density of charge carrier

121 .
When temperature is above ferromagnetic Curie temperature, a ferromagnetic material
A)
becomes diamagnetic material
B)
becomes a paramagnetic material
C)
becomes a very strong ferromagnetic material
D)
None of the above

Correct Answer :   becomes a paramagnetic material

Explanation : Above ferromagnetic Curie temperature, ferro-magnetic material behaves as a paramagnetic material.

122 .
A magnet does not attract
A)
iron
B)
nickel
C)
iron and copper
D)
copper

Correct Answer :   copper

123 .
When a potential is applied across an intrinsic semiconductor, holes flow
A)
towards positive terminal
B)
away from positive terminal
C)
in the external circuit only
D)
None of the above

Correct Answer :   away from positive terminal

124 .
Silicon and germanium are elements in the
A)
second column of periodic table
B)
third column of periodic table
C)
fourth column of periodic table
D)
fifth column of periodic table

Correct Answer :   fourth column of periodic table

125 .
Which of the following is used in temperature alarm circuits?
A)
Thermistor
B)
Transistor
C)
Varistor
D)
Photoconductor

Correct Answer :   Thermistor

126 .
n type semiconductors
A)
are negatively charged
B)
are produced phosphorus as impurity is added to silicon
C)
are produced when indium as impurity is added to germanium
D)
None of the above

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

Explanation : n type semiconductors are produced by adding pentavalent material like phosphorus to silicon.

127 .
The most important primary force of attraction in the formation of solids is
A)
electrostatic
B)
electromagnetic
C)
quantum-electrostatic
D)
quantum electromagnetic

Correct Answer :   electrostatic

128 .
Fleming's left hand rule is used to find
A)
direction of induced emf
B)
direction of flux in solenoid
C)
direction of force on a current carrying conductor
D)
direction of magnetic field due to a current carrying conductor

Correct Answer :   direction of force on a current carrying conductor

129 .
A dielectric material must be
A)
insulator
B)
resistor
C)
semiconductor
D)
good conductor

Correct Answer :   insulator

Explanation : Any material other than insulator will short-circuit the plates.

130 .
The maximum temperature limit of class B insulation is
A)
90°C
B)
105°C
C)
120°C
D)
130°C

Correct Answer :   130°C

131 .
The resistance of a superconductor is
A)
low
B)
zero
C)
very low
D)
None of the above

Correct Answer :   zero

132 .
For a superconductor, magnetisation M in a field H is
A)
- I
B)
- H
C)
zero
D)
extremely small

Correct Answer :   - H

133 .
The probability of recombination of electrons and holes in a semiconductor is proportional to
A)
density of holes
B)
density of electrons
C)
density of electrons and holes
D)
None of the above

Correct Answer :   density of electrons and holes

134 .
If temperature is increased, the temperature coefficient of a metal
A)
decreases
B)
increases
C)
remains constant
D)
may increase or decrease

Correct Answer :   decreases

135 .
Automobile ignition systems use the principle of
A)
capacitance
B)
resistance
C)
self inductance
D)
mutual inductance

Correct Answer :   mutual inductance

Explanation : A high voltage is induced due to mutual inductance because the number of turns in secondary coil is very high.

136 .
The application of magnetic field to superconducting material
A)
increases transition temperature
B)
has no effect on transition temperature
C)
may increase or decrease the transition temperature
D)
decreases transition temperature

Correct Answer :   decreases transition temperature

137 .
In a valence crystal, the valence electrons
A)
are not shared
B)
are shared by all atoms
C)
are shared between neighbouring atoms
D)
Any of the above

Correct Answer :   are shared between neighbouring atoms

Explanation : In true valence crystals the binding between the atoms is accomplished by the sharing of valence electrons.

This sharing can only be between neighbouring atoms only.

138 .
The materials having low retentivity are suitable for making
A)
weak magnets
B)
temporary smagnets
C)
permanent magnets
D)
both temporary and permanent magnets

Correct Answer :   temporary smagnets

139 .
Transformer oil is
A)
refined mineral oil
B)
refined vegetable oil
C)
mixture of vegetable and mineral oil
D)
None of the above

Correct Answer :   refined mineral oil

140 .
The resistance of a metallic wire would
A)
decrease as f increase
B)
increase as f increase
C)
remains the same at all frequencies
D)
increase with f up to a certain frequency and then decrease

Correct Answer :   increase as f increase

141 .
The capacitance of a capacitor is not affected by
A)
area of plates
B)
thickness of plates
C)
distance between plates
D)
None of the above

Correct Answer :   thickness of plates

Explanation : Capacitance depends on area, distance and ∈r but not on thickness of plates.

142 .
Hall effect is observed in a specimen (metal or semi- conductor) when it is carrying current and is placed in a magnetic field. The resultant electric field inside the specimen is
A)
normal to both current and magnetic field
B)
in the same direction as current
C)
in a direction anti parallel to magnetic field
D)
None of the above

Correct Answer :   normal to both current and magnetic field

143 .
The charge per proton is
A)
0.6 x 10⁻¹⁹ C
B)
1.6 x 10⁻¹⁹ C
C)
2.6 x 10⁻¹⁹ C
D)
1.6 x 10⁻¹³ C

Correct Answer :   1.6 x 10⁻¹⁹ C

Explanation : Because charge on proton is positive but numerically equal to that on electron.

144 .
For a permanent magnetic material
A)
area of hysteresis loop should be small
B)
initial relative permeability should be high
C)
the residual induction and coercive field should be small
D)
the residual induction and coercive field should be large

Correct Answer :   the residual induction and coercive field should be large

Explanation : Materials suitable for permanent magnet have large hysteresis loop.

Hence residual and coercive field are large.

145 .
In a coaxial cable, braided copper is used for
A)
shield
B)
jacket
C)
dielectric
D)
conductor

Correct Answer :   shield

146 .
The attraction between the nucleus and valence electron of copper atom is
A)
zero
B)
weak
C)
strong
D)
either zero or strong

Correct Answer :   weak

Explanation : The valence electron, in copper atom, can be easily detached from nucleus.

147 .
If the temperature of an extrinsic semiconductor is increased so that the intrinsic carrier concentration is doubled, then
A)
the majority carrier density is doubled
B)
the minority carrier density is doubled
C)
the minority carrier density becomes 4 times the original value
D)
both the majority and minority carrier densities double

Correct Answer :   both the majority and minority carrier densities double

Explanation : As the intrinsic carrier concentration is doubled, the concentration of both electrons and holes is doubled.

148 .
The units of μ0 and μr are
A)
H/m for both
B)
H/m for μr and no units for μ0
C)
H/m for μ0 and no units for μr
D)
Wb/m for μ0 and no units for μr

Correct Answer :   H/m for μ0 and no units for μr

149 .
Hydrogen is used in
A)
MCB
B)
circuit breakers
C)
large size generators
D)
large size transformers

Correct Answer :   large size generators

150 .
Dielectric constant of transformer oil is about
A)
1
B)
4
C)
10
D)
20

Correct Answer :   4

151 .
In carbon resistor colour code, the third band is red. It indicates
A)
two zeros
B)
three zeros
C)
multiplier is 0.01
D)
multiplier is 0.1

Correct Answer :   two zeros

152 .
A piece of iron is placed in a magnetic field
A)
the magnetic field will not be affected
B)
any of the above depending on type of iron
C)
the magnetic lines of force will bend away from the piece
D)
the magnetic lines of force will bend to pass through the piece

Correct Answer :   the magnetic lines of force will bend to pass through the piece

153 .
Ferromagnetic materials
A)
can be used even at microwave frequencies
B)
have resistivity very high as compared to that of iron
C)
shows spontaneous magnetisation below a certain temperature
D)
All of the above

Correct Answer :   All of the above

154 .
The number of valence electrons in acceptor impurity are
A)
1
B)
3
C)
4
D)
5

Correct Answer :   3

155 .
Thermistor is used in
A)
temperature control
B)
temperature measurement
C)
high temperature alarm circuits of devices
D)
All of the above

Correct Answer :   All of the above

156 .
Even at room temperature, an intrinsic semiconductor has some holes. These holes are due to
A)
doping
B)
electron
C)
thermal energy
D)
free electrons

Correct Answer :   thermal energy

157 .
In carbon resistor colour code, if the third band is of silver, it indicates
A)
multiplier is 0.01
B)
multiplier is 0.1
C)
tolerance is ± 5%
D)
that three zeros are to be added to indicate the resistance value

Correct Answer :   multiplier is 0.01

158 .
At a temperature of about 1 K, aluminium is a
A)
superconductor
B)
insulator
C)
conductor
D)
photoconductor

Correct Answer :   superconductor

159 .
An electron shell corresponding to principal quantum number n can contain a maximum of
A)
n² electrons
B)
2n² electrons
C)
2n electron
D)
None of the above

Correct Answer :   2n² electrons

Explanation : The electron shell corresponding to the principal quantum number can contain no more than 2n² electrons.

160 .
A sheet of bakelite is inserted between the plates of an air capacitor. The capacitance will
A)
increase
B)
decrease
C)
remain the same
D)
may increase or decrease

Correct Answer :   increase

161 .
At T = 0, the resistivity of a perfect single crystal of a metal is
A)
0
B)
low
C)
high
D)
finite

Correct Answer :   0

162 .
In a polyatomic gas, the types of polarization which exist together are
A)
electronic and ionic
B)
ionic and orientational
C)
electronic and orientational
D)
electronic, orientational and ionic

Correct Answer :   electronic, orientational and ionic

163 .
Which of the following is used in lightning arresters?
A)
Transistor
B)
Thermistor
C)
Varistor
D)
Photoconductor

Correct Answer :   Varistor

164 .
High frequency inductors and capacitors are commonly plated with silver. The main purpose of this is to
A)
reduce dc resistance
B)
reduce ac resistance
C)
increase ac resistance
D)
increase dc resistance

Correct Answer :   reduce ac resistance

165 .
In its lowest state, the electron is bound to the field of proton by an energy equal to
A)
0.2 eV
B)
13.6 eV
C)
51.2 eV
D)
100.5 eV

Correct Answer :   13.6 eV

166 .
In a ferromagnetic material, the internal field seen by a dipole is
A)
equal to applied field plus a contribution from neighbouring dipoles
B)
equal to applied field
C)
equal to or less than applied field
D)
equal to applied field minus a contribution from neighbouring dipoles

Correct Answer :   equal to applied field plus a contribution from neighbouring dipoles

167 .
The iron core of a coil is removed so that it becomes an air cored coil. Its inductance will
A)
increase
B)
decrease
C)
remain the same
D)
may increase or decrease

Correct Answer :   decrease

168 .
For small size high frequency coils, the most common core material is
A)
steel
B)
ferrite
C)
air
D)
powdered iron

Correct Answer :   air

169 .
A circular sphere mile is the area of cross-section of a wire
A)
having a radius equal to 1 miles
B)
having a circumference equal to 1 miles
C)
having a circumference equal to 0 miles
D)
having a diameter equal to 1 miles

Correct Answer :   having a diameter equal to 1 miles

170 .
Magnetic hysteresis phenomenon is explained by
A)
domain rotation
B)
motion of domain walls
C)
motion of domain walls and domain rotation
D)
None of the above

Correct Answer :   motion of domain walls and domain rotation

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