EEE - RC Circuits Quiz (or) MCQ | Questions and Answers

1 .

The time constant of an R-C circuit is?

A)

R

B)

C

C)

RC

D)

R/C

Correct Answer : RC

Explanation : The time constant of an R-C circuit is RC and it is denoted by τ and the value of τ in dc response of R-C circuit is RC sec.

2 .

After how many time constants, the transient part reaches more than 99 percent of its final value?

A)

2

B)

3

C)

4

D)

5

Correct Answer : 5

Explanation : After five time constants, the transient part of the response reaches more than 99 percent of its final value.

3 .

The expression of current in R-C circuit is?

A)

i=(V/R)expâ¡(t/RC)

B)

i=(V/R)expâ¡(-t/RC)

C)

i=(V/R)-exp(â¡t/RC)

D)

i=(V/R)-expâ¡(-t/RC)

Correct Answer : i=(V/R)expâ¡(-t/RC)

Explanation : The particular solution of the current equation is zero. So the expression of current in R-C circuit is i=(V/R)expâ¡(-t/RC).

4 .

In an R-C circuit, when the switch is closed, the response _________

A)

rises with time

B)

decays with time

C)

do not vary with time

D)

first increases and then decreases

Correct Answer : decays with time

Explanation : In a R-C circuit, when the switch is closed, the response decays with time that is the response V/R decreases with increase in time.

5 .

A positive angle of 30Â° is equivalent to a negative angle of

A)

-330Â°

B)

-180Â°

C)

-60Â°

D)

-30Â°

Correct Answer : -330Â°

6 .

Apparent power is expressed in watts.

A)

True

B)

False

C)

--

D)

--

Correct Answer : False

7 .

The complex number 6 + j6 is equivalent to

A)

6 ∠45°

B)

36 ∠45°

C)

8.48 ∠45°

D)

8.48 ∠90°

Correct Answer : 8.48 ∠45°

8 .

In a series RC circuit, when the frequency and the resistance are halved, the impedance

A)

Doubles

B)

Is halved

C)

Is reduced to one-fourth

D)

Cannot be determined without values

Correct Answer : Cannot be determined without values

9 .

A 2 kΩ resistor is in series with a 0.015 µF capacitor across a 15 kHz ac source. What is the magnitude of the total impedance and the phase angle?

A)

73.4 Ω and θ = -19.5°

B)

707 Ω and θ = -19.5°

C)

2121 Ω and θ = -19.5°

D)

734 Ω and θ = -38.9°

Correct Answer : 2121 Ω and θ = -19.5°

10 .

What is the angular difference between +j4 and -j4?

A)

180Â°

B)

90Â°

C)

30Â°

D)

270Â°

Correct Answer : 180Â°

11 .

A 47 Ω resistor and a capacitor with a capacitive reactance of 120 Ω are in series across an ac source. What is the circuit impedance, Z?

A)

12.9 Ω

B)

73 Ω

C)

167 Ω

D)

129 Ω

Correct Answer : 129 Ω

12 .

In the complex plane, the number 4 + j3 is located in the

A)

First quadrant

B)

Second quadrant

C)

Third quadrant

D)

Fourth quadrant

Correct Answer : First quadrant

13 .

In the complex plane, the number 14 - j5 is located in the

A)

First quadrant

B)

Second quadrant

C)

Third quadrant

D)

Fourth quadrant

Correct Answer : Fourth quadrant

14 .

A 470 Ω resistor and a 0.2 µF capacitor are in parallel across a 2.5 kHz ac source. The admittance, Y, in rectangular form, is

A)

212 Ω

B)

318.3 Ω

C)

2.12 mS + j3.14 mS

D)

3.14 mS + j2.12 mS

Correct Answer : 2.12 mS + j3.14 mS

15 .

A 6 kHz sinusoidal voltage is applied to a series RC circuit. The frequency of the voltage across the resistor is

A)

0 Hz

B)

6 kHz

C)

12 kHz

D)

18 kHz

Correct Answer : 6 kHz

16 .

A complex number represents a phasor quantity.

A)

True

B)

False

C)

--

D)

--

Correct Answer : True

17 .

The resistor voltage is always out of phase with the current.

A)

True

B)

False

C)

--

D)

--

Correct Answer : False

18 .

When the frequency of the voltage applied to a series RC circuit is increased, the phase angle

A)

Increases

B)

Decreases

C)

Becomes erratic

D)

Remains the same

Correct Answer : Decreases

19 .

In a parallel RC circuit, there is 100 mA through the resistive branch and 100 mA through the capacitive branch. The total rms current is

A)

141 mA

B)

100 mA

C)

200 mA

D)

282 mA

Correct Answer : 141 mA

20 .

In a lag network, the output voltage lags the input voltage in phase.

A)

True

B)

False

C)

--

D)

--

Correct Answer : True

21 .

In a series RL circuit, 12 V rms is measured across the resistor, and 14 V rms is measured across the inductor. The peak value of the source voltage is

A)

2 V

B)

18.4 V

C)

20 V

D)

26.0 V

Correct Answer : 26.0 V

22 .

Total current in an RC circuit always leads the source voltage

A)

True

B)

False

C)

--

D)

--

Correct Answer : True

23 .

The complex number 40 ∠ 55° is equivalent to

A)

55 + j55

B)

45.88 + j65.52

C)

40 + j40

D)

22.94 + j32.76

Correct Answer : 22.94 + j32.76

24 .

A 2 kΩ resistor and a 0.002 µF capacitor are in series across an ac source. Current in the circuit is 6.50 mA. The true power is

A)

13 mW

B)

84.5 mW

C)

130 mW

D)

845 mW

Correct Answer : 84.5 mW

25 .

A series R-C circuit consists of resistor of 10 and capacitor of 0.1F as shown in the figure. A constant voltage of 20V is applied to the circuit at t = 0. What is the current in the circuit at t = 0?

A)

1

B)

2

C)

3

D)

4

Correct Answer : 2

Explaination : At t = 0, switch S is closed. Since the capacitor does not allow sudden changes in voltage, the current in the circuit is i = V/R = 20/10 = 2A. At t = 0, i = 2A.

26 .

The expression of current obtained from the circuit in terms of differentiation from the circuit shown below?

A)

di/dt+i=1

B)

di/dt+i=2

C)

di/dt+i=3

D)

di/dt+i=0

Correct Answer : di/dt+i=0

Explaination : By applying Kirchhoff’s law, we get

27 .

Determine the voltage across the capacitor in the circuit shown below is?

A)

V_C = 60(1-e^-t)V

B)

V_C = 60(1+e^t)V

C)

V_C = 60(1-e^t)V

D)

V_C = 60(1-e^t)V

Correct Answer : V_C = 60(1-e^-t)V

Explaination : The expression of voltage across capacitor in the circuit V_C = V(1-e^-t/RC) = 20(1-e^-t)V.

28 .

When the frequency of the voltage applied to a series RC circuit is decreased, the impedance

A)

Increases

B)

Decreases

C)

Doubles

D)

Remains the same

Correct Answer : Increases

29 .

The circuit phase angle is the angle between the total current and the applied (source) voltage.

A)

True

B)

False

C)

--

D)

--

Correct Answer : True

30 .

A capacitor with 150 ohm of capacitive reactance is across an ac source. The impedance, expressed in polar form, is

A)

Z = 150 ohm

B)

Z = 150 ∠90° ohm

C)

Z = 150 ∠-90° ohm

D)

Z = 150 ∠180° ohm

Correct Answer : Z = 150 ∠-90° ohm

31 .

A 12 kΩ resistor is in series with a 0.02 µF capacitor across a 1.2 kHz ac source. If the current is expressed in polar form as I = 0.3 ∠0° mA, what is the source voltage expressed in polar form?

A)

0.411 V

B)

4.11 V

C)

45.6 V

D)

411.3 V

Correct Answer : 4.11 V

32 .

For a certain load, the true power is 150 W and the reactive power is 125 VAR. The apparent power is

A)

19.52 W

B)

25 W

C)

195.2 W

D)

275 W

Correct Answer : 195.2 W

33 .

The polar form of a complex number consists of a real part and a j part.

A)

True

B)

False

C)

--

D)

--

Correct Answer : False

34 .

In a series RC circuit, 12 V(rms) is measured across the resistor and 15 V(rms) is measured across the capacitor. The rms source voltage is

A)

1.9 V

B)

3 V

C)

19.2 V

D)

27 V

Correct Answer : 19.2 V

35 .

An ac circuit consists of a resistor and a capacitor. To increase the phase angle above 45°, the following condition must exist:

A)

R < Xc

B)

R = Xc

C)

R > Xc

D)

R = 5Xc

Correct Answer : R < Xc

36 .

What is the value of the hypotenuse of a right triangle whose sides are 12 and 18?

A)

2.16

B)

3.46

C)

4.24

D)

21.63

Correct Answer : 21.63

37 .

Positive numbers can be represented by points to the right of the origin on the horizontal axis of a graph.

A)

True

B)

False

C)

--

D)

--

Correct Answer : True

38 .

Point +4 on the complex plane is

A)

4 units above the origin on the j axis

B)

4 units below the origin on the j axis

C)

4 units right of the origin on the real axis

D)

4 units left of the origin on the real axis

Correct Answer : 4 units right of the origin on the real axis

39 .

A 120 Ω resistor is in parallel with a capacitor with a capacitive reactance of 40 Ω. Both components are across a 12 V ac source. What is the magnitude of the total impedance?

A)

3.7 Ω

B)

37.9 Ω

C)

14,400 Ω

D)

4,800 Ω

Correct Answer : 37.9 Ω

40 .

A 47 Ω resistor and a capacitor with 150 Ω of capacitive reactance are in series across an ac source. The impedance, expressed in rectangular form, is

A)

Z = 197 Ω

B)

Z = 103 Ω

C)

Z = 47 Ω - j150 Ω

D)

Z = 47 Ω + j150 Ω

Correct Answer : Z = 47 Ω - j150 Ω

41 .

The current equation in the circuit shown below is?

A)

i=2(e^-2t)A

B)

i=2(e^2t)A

C)

i=2(-e^-2t)A

D)

i=2(-e^2t)A

Correct Answer : i=2(e^-2t)A

Explaination : At t = 0, switch S is closed. Since the capacitor does not allow sudden changes in voltage, the current in the circuit is i = V/R = 20/10 = 2A. At t = 0, i = 2A. The current equation is i=2(e^-2t)A.

42 .

The expression of voltage across resistor in the circuit shown below is?

A)

V_R = 20(e^t)V

B)

V_R = 20(e^-t)V

C)

V_R = 20(-e^t)V

D)

V_R = 20(e^-t)V

Correct Answer : V_R = 20(e^-t)V

Explaination : The expression of voltage across resistor in the circuit is V_R = iR =(2(e^-t))×10=20(e^-t)V.

43 .

The power factor (PF) indicates how much of the apparent power is true power.

A)

True

B)

False

C)

--

D)

--

Correct Answer : True

44 .

A resistor and a capacitor are in series across a 20 V ac source. Circuit impedance is 4.33 kΩ. Current flow in the circuit is

A)

4.6 mA

B)

9.2 mA

C)

92 mA

D)

460 mA

Correct Answer : 4.6 mA