Free Printable Chapter 20: Alternating Current

1.

A pure resistor is connected to an a.c. source where its current is given by I=5.0 sin 628t. Which of the following statements is not true about the circuit?

a)

The peak value of current flowing through the resistor is 5.0 A

b)

The root mean square current flowing through the resistor is 3.5 A

c)

The frequency of the current flowing through across the resistor is 120 Hz

d)

The equivalent direct current which gives the same average heating power in the resistor is 3.5 A

2.

Which of the following diagrams is the correct phasor diagram for V_R,V_Land V?

a)

b)

c)

d)

3.

The reactance Xc of the capacitor and the resistance R are shown in the phasor diagram. Which of the following statements describes Z and $\phi$ correctly?

a)

Z is the impedance of the combined R and $X_c$
$\phi$ is the phase angle where current leads the voltage

b)

Z is the impedance of the combined R and $X_c$
$\phi$ is the phase angle where voltage leads the current

c)

Z is the reactance of the resistor
$\phi$ is the phase angle where R leads Z.

d)

Z is the impedance of the combined R and $X_c$
$\phi$ is the phase angle where Z leads R

4.

All of the following have the same units except:

a)

inductance.

b)

capacitive reactance.

c)

impedance.

d)

resistance.

5.

A resistor is connected to an AC power supply. On this circuit, the current

a)

leads the voltage by 90°.

b)

lags the voltage by 90°.

c)

is in phase with the voltage.

d)

none of the given answers

6.

A pure inductor is connected to an AC power supply. In this circuit, the current

a)

leads the voltage by 90°.

b)

lags the voltage by 90°.

c)

is in phase with the voltage.

d)

none of the given answers.

7.

If the frequency of the AC voltage across an inductor is doubled, the inductive reactance of that inductor

a)

increases to 4 times its original value.

b)

increases to twice its original value.

c)

decreases to one-half its original value.

d)

decreases to one-fourth its original value.

8.

What is the phase angle between the voltages of the inductor and capacitor in a RLC series circuit?

a)

zero

b)

90°

c)

180°

d)

270°

9.

The formula for inductive reactance is

a)

$\frac{1}{\omega L}$

b)

$\omega C$

c)

$\frac{1}{\omega C}$

d)

$\omega L$

10.

The equations for alternating emf and alternating current in a circuit containing capacitor are

a)

$V\ =\ V_0\ \sin\ \omega t,\ I\ =\ I_0\ \sin\left(\omega t-\frac{\pi}{2}\right)$

b)

$V=V_0\ \sin\ \omega t\ ,\ I\ =\ I_0\ \sin\left(\omega t\ +\frac{\pi}{2}\right)$

c)

$V\ =\ V_0\ \sin\omega t,\ I\ =I_0\ \sin\ \omega t$

d)

$V\ =\ V_0\ \sin\left(\omega t\ +\frac{\pi}{2}\right),\ I\ =\ I_0\ \sin\ \omega t$

11.

What happens at resonance?

a)

Current is maximum

b)

Impedance is maximum

c)

Resistance is maximum

d)

Power factor is maximum

12.

Average power dissipated in an ideal inductor in a.c. circuit is:

a)

Infinite

b)

100

c)

0

d)

1

13.

AC stands for

a)

Air-condition

b)

Direct Current

c)

Alternating Current

d)

Alternating Voltage

14.

The electricity in our house is

a)

AC

b)

DC

c)

BC

d)

AD

15.

An electric current flowing in one direction only

a)

voltage

b)

parallel current

c)

direct current

d)

electric current

16.

The power factor of an RLC circuit is defined as cos ∅ = R/Z, but the phase angle can also be calculated from ________.

a)

sin ∅ = (XL - XC)/Z

b)

sin ∅ = (XL - XC)/RZ

c)

sin ∅ = Z/(XL - XC)

d)

sin ∅ = RZ/(XL - XC)

17.

A capacitor 120 µF is connected to an AC source of 6 V with frequency 100 Hz. If the frequency is increased to 200 Hz, the reactance of the capacitor will be

a)

half the original value.

b)

same as the original value.

c)

two times the original value.

d)

the reciprocal of the original value.

18.

What is alternating current

a)

the process of inducing an emf (voltage) with a change in magnetic flux

b)

Electric currents whose direction and magnitude change periodically depending on time are called alternating current

c)

Steady current which delivers the same average power as the a.c. to a resistive load.

d)

Making a rectified current more steady (or smooth) by placing a capacitor in parallel with the resistor

19.

Which one of the below AC parameters show the effective Dc value?

a)

Peak Value

b)

RMS value

c)

Peak to peak value

d)

Frequency

20.

a)

A

b)

B

c)

C

d)

D

21.

a)

A

b)

B

c)

C

d)

D

22.

Alternating current changes

a)

Its magnitude as well as direction

b)

Only direction but not magnitude

c)

Only magnitude but not direction

d)

Does not change anything

23.

The instantaneous value of alternating voltage is

a)

$V\ =\ V_0\ \sin\ 2\pi ft$

b)

$V\ =\ V_0\ \sin\ 2ft$

c)

$V\ =\ V_0\ \sin\ 2\pi\omega t$

d)

$V\ =\ V_0\ \sin\ ft$

24.

The waveform of alternating current/voltage is:

a)

Stright line

b)

Curved

c)

Sinusoidal

d)

cotangent

25.

The highest value reached by the voltage or current in one cycle is called:

a)

Instantaneous value

b)

Peak to peak value

c)

Peak value

d)

Root mean square value

26.

In case of phasor diagram the vector rotates

a)

Clockwise

b)

anticlockwise

c)

Remain stationary

d)

None

27.

In pure resistive AC circuit, instantaneous value of voltage or current:

a)

Current lags behind voltage

b)

Current leads voltage by 90

c)

Both are in-phase

d)

Voltage leads current by 90

28.

The behavior of resistance in pure resistor is frequency

a)

Dependent

b)

Independent

c)

No response

d)

None of these

29.

$P=\ I_{rms}V_{rms}\ \cos\ \phi$

The power dissipation in AC circuit is given above. What does cos phi represent?

a)

Phase factor

b)

Gain factor

c)

Loss factor

d)

Power factor

30.

Power dissipation in pure inductive or in a pure capacitive circuit is:

a)

Infinite

b)

Zero

c)

Minimum

d)

Maximum

31.

The circuit in which current and voltage are in phase, the power factor is:

a)

Zero

b)

One

c)

Two

d)

Three

32.

At resonance RLC series circuit shows the behavior of:

a)

Pure resistive circuit

b)

Pure capacitive circuit

c)

Pure inductive circuit

d)

Pure RLC circuit

33.

At resonance, the phase angle for RLC series resonance circuit equals:

a)

$0\degree$

b)

$90\degree$

c)

$180\degree$

d)

$270\degree$

34.

The condition of resonance reached when

a)

$X_C\ >\ X_L$

b)

$X_L\ >X_C$

c)

$X_C\ =X_L$

d)

$X_C\ \ne X_L$

35.

At higher frequencies, which of the following plays a dominant role in RLC series circuit

a)

Resistor

b)

Capacitor

c)

Inductor

d)

Transistor

36.

The impedance Z can be expressed as:

a)

$V_{rms}\ +\ I_{rms}$

b)

$V_{rms}\ -\ I_{rms}$

c)

$\frac{V_{rms}}{I_{rms}}$

d)

$\frac{I_{rms}}{V_{rms}}$

37.

The combine opposition of resistor, capacitor and inductor is called

a)

Reactance

b)

Resistor

c)

Impedance

d)

Capacitance

38.

the number of complete oscillations of the signal per unit time Is defined by?

a)

period

b)

peak current

c)

frequency

39.

The power factor is the ratio of __________________ power to _________________ power.

a)

true and apparent

b)

true and real

c)

positive and negative

d)

factor and real

40.

When frequency decreases, capacitive reactance _____.

a)

increases

b)

decreases

c)

remains the same

d)

may increase or decrease

41.

The power factor can be defined as the ratio of true power to _____.

a)

apparent power

b)

total resistance

c)

total current

d)

reactive power

42.

The r.m.s value of an alternating current is given by steady (D.C) current which when flowing through a given circuit for a given time produces

a)

the more heat than produced by A.C when flowing through the sam circuit

b)

the less heat than produced by A.C when flowing through the sam circuit

c)

the same heat than produced by A.C when flowing through the same circuit

43.

What does RC stand for?

a)

Remote Control

b)

Radio Control

c)

Resistor Capacitor

d)

Rotary Club

44.

Which one of the following statements is true?

a)

In a capacitor, current lags voltage by 90°

b)

In a resistor, voltage lags current by 90°

c)

In a capacitor, voltage lags current by 90°

d)

In a resistor, current lags voltage by 90°

45.

The unit of inductive reactance is :

a)

Ohm

b)

Ampere

c)

Farad

d)

Henry

46.

Inductive reactance results in a current that

a)

Leads the voltage by 90°

b)

Is in phase with the voltage

c)

Leads the voltage by π rad

d)

Lags the voltage by π/2 rad

47.

In RLC circuit, If R is the resistance, XL is the inductive reactance and XC is the capacitive reactance, the impedance Z of the circuit is:

a)

b)

c)

d)

48.

What words are missing from the following statement? The impedance of a series RCL circuit at resonance will be _______ and equal to the circuit _______ .

a)

Minimum and resistance.

b)

Maximum and resistance.

c)

Minimum and reactance.

d)

Maximum and reactance

49.

Which is the correct equation of

V_{rms}

?

a)

$V_{rms}=V_o$

b)

$V_{rms}=\frac{\sqrt{2}}{V_o}$

c)

$V_{rms}=\frac{V_o}{\sqrt{2}}$

d)

$V_{rms}=\frac{V_o}{\sqrt{2}}\sin\ 2t$

50.

The maximum voltage across the inductor in an ac circuit is given by

a)

$V_o=I_oX_L$

b)

$V_o=I_{rms}X_L$

c)

$V_{rms}=I_{rms}X_L$

d)

$V_o=I_oL$

51.

The relationship between two alternating quantities can be represented by using

a)

Phasor diagram

b)

Sinusoidal graph

c)

phasor diagram and sinusoidal graph

d)

none of above

Chapter 20: Alternating Current

Total questions: 51

Worksheet time: 26mins

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