Free Printable AC CIRCUITS OBJECTIVES

1.

the period of the wave

a)

the same as frequency

b)

time required to complete one cycle

c)

expressed in amperes

d)

none of the above

2.

the r.m.s. value of sine wave is equal to

a)

0.637 max. value

b)

0.506 max.value

c)

0.707 max.value

d)

1.414 max.value

3.

the rms value mean value is the same in the case of

a)

triangular wave

b)

square wave

c)

sine wave

d)

half wave rectified sine wave

4.

in the case of an unsymmetrical alternating current the average value must always be Taken over

a)

unsymmetrical part of the wave form

b)

the quarter cycle

c)

the half cycle

d)

the whole cycle

5.

what is the form factor of half wave rectified sinusoidal wave?

a)

1.57

b)

1.11

c)

1.0

d)

1.15

6.

in a pure inductive circuit

a)

the current is in phase with the voltage

b)

the current lags the voltage by 90 degrees.

c)

the currents lead the voltage by 90 degrees,

d)

the current can lead or lag the voltage by 90 degrees.

7.

which of the following circuit component opposes the change in the circuit voltage?

a)

inductance

b)

conductance

c)

capacitance

d)

resistance

8.

in a circuit containing R, L and C, power loss can take place in

a)

C only

b)

R only

c)

L only

d)

all above

9.

in a pure inductive if the supply frequency is reduced to 1/2. the current will

a)

be reduced by half

b)

be doubled

c)

be four times as high

d)

be reduce to one fourth

10.

in an AC circuit. a low value of kVAR compared with kW indicates

a)

low frequency

b)

unity power factor

c)

high power factor

d)

maximum load current

11.

in a purely inductive circuit

a)

actual power is zero

b)

reactive power is zero

c)

apparent power is zero

d)

none of above is zero

12.

power factor of electric bulb is

a)

zero

b)

leading

c)

lagging

d)

unity

13.

the best place to install a capacitor is

a)

across the terminals of the inductive load

b)

far away from the inductive load

c)

very near to inductive load

d)

any where

14.

capacitors for power factor correction are rated in

a)

kW

b)

kV

c)

kVA

d)

kVAR

15.

the quality factor of R-L-C circuit will increase if

a)

R increases

b)

impedance increases

c)

R decreases

d)

voltage increases

16.

a series R-L-C circuit draws current at leading power factor at

a)

more than resonant frequency

b)

less than resonant frequency

c)

resonant frequency

d)

none of the above

17.

in as parallel resonant circuit, the impedance of the circuit is

a)

maximum

b)

zero

c)

minimum

d)

infinite

18.

in as series resonant circuit, the current of the circuit is

a)

maximum

b)

zero

c)

minimum

d)

infinite

19.

an LC series circuit with an inductance L an a capacitor C has an oscillation frequency of f. Two inductors, each with inductance L, and two capacitors, each with capacitance C, are all wired in series and the circuit is completed. The oscillation frequency is ____.

a)

$\frac{f}{4}$

b)

f

c)

2f

d)

$\frac{f}{2}$

20.

in an oscillating LC circuit, the maximum charge on the capacitor is Q. The charge on capacitor when the energy is stored equally between electric and magnetic field is:

a)

$\frac{Q}{2}$

b)

$\frac{Q}{\sqrt[]{2}}$

c)

$\frac{Q}{\sqrt[]{3}}$

d)

Q

21.

a charged capacitor and an inductor are connected in series. At time t = 0 the current is zero, but the capacitor is charged. if T is the period of the resulting oscillations, the next time after t = 0 that the current is a maximum is:

a)

T

b)

$\frac{T}{4}$

c)

$\frac{T}{2}$

d)

2T

22.

which of the following value of alternating voltage should insulation absolutely withstand?

a)

the average value

b)

the rms value

c)

the peak value

d)

half the effective value

23.

the voltage of domestic supply is 220 V. This figure represents

a)

mean value

b)

rms value

c)

peak value

d)

half the effective value

24.

for the same peak value which of the following wave will have the highest rms value?

a)

square wave

b)

half wave rectifier sine wave

c)

triangular wave

d)

sine wave

25.

in a pure resistive circuit

a)

current lags the voltage by 90 degrees.

b)

currents lead the voltage by 90 degrees.

c)

current can lead or lag the voltage by 90 degrees.

d)

current is in phase with the voltage

26.

which of the following AC device is used to measure the angle between the voltage and its current?

a)

reactive meter

b)

power factor meter

c)

demand meter

d)

phase angle meter

27.

inductance of coil

a)

is unaffected by the supply frequency

b)

decrease with the increase in supply frequency

c)

increases with the increase in supply frequency

d)

becomes zero with the increase in supply frequency

28.

in a purely inductive circuit

a)

actual power is zero

b)

reactive power is zero

c)

apparent power is zero

d)

none of the above is zero

29.

power factor of electric bulb is

a)

zero

b)

leading

c)

lagging

d)

unity

30.

a pure inductance connected across 250 V, 50 Hz supply consumes 100 W. This consumption can be attributed to

a)

the big size of the inductor

b)

the reactance of the inductor

c)

the current flowing in the inductor

d)

the statement given is false

31.

the ratio of active power to apparent power is known as ___ factor

a)

demand

b)

load

c)

power

d)

form

32.

all definition of power factor of a series R-L-C circuit are connected except

a)

ratio of net reactance and impedance

b)

ratio of kW and kVA

c)

ratio of R and Z

d)

ratio of W and VA

33.

what will be the phase angle between two alternating waves of equal frequency, when one wave attains maximum value the other is at zero value?

a)

0 deg.

b)

45 deg.

c)

90 deg.

d)

180 deg.

34.

in a R-L-C circuit the impedance is given by

a)

$Z=R+X_L-X_C$

b)

$Z=R-X_L+X_C$

c)

$Z=\sqrt[]{\left(R+X_L\right)^2+X_C^2}$

d)

$Z=\sqrt[]{R^2+\left(X_L-X_C^{ }\right)^2}$

35.

poor power factor results to the following except

a)

reduces load handling capability of electrical system

b)

results in more power losses in the electrical system

c)

overloads alternators, transformers and distribution lines

d)

result in less voltage drop in the line

36.

in as series resonant circuit, the impedance of the circuit is

a)

maximum

b)

zero

c)

minimum

d)

infinite

37.

in a series circuit on resonance, following will occur except

a)

$V=V_R$

b)

Z = R

c)

$X_L=X_C$

d)

$V_L=V_R$

38.

in a series resonant circuit, the voltage across the circuit is the same as the voltage across

a)

inductance

b)

resistance

c)

capacitance

d)

none of the above

39.

at half-power points of a resonance curve, the current is __ times the maximum current

a)

$\frac{1}{2}$

b)

$\frac{1}{\sqrt[]{2}}$

c)

$\sqrt[]{2}$

d)

2

40.

the ratio of the bandwidth to the resonance frequency is called the __ of the circuit

a)

impedance

b)

quality factor

c)

susceptance

d)

selectivity

41.

the dynamic impedance of an R-L and C parallel circuit at resonance is __ ohm

a)

$\frac{R}{LC}$

b)

$\frac{C}{LR}$

c)

$\frac{LC}{R}$

d)

$\frac{L}{CR}$

42.

the phase displacement between phasors in polyphase system is always

a)

90 deg.

b)

360 deg. divide by the number of phases

c)

120 deg.

d)

60 deg.

43.

in a balanced 3-phase voltage generator, the different phase voltages are ___ degrees apart.

a)

120

b)

240

c)

60

d)

30

44.

in a balanced 3 phase wye connected system, the line voltage and the corresponding phase voltage are displaced from each other by ___.

a)

0

b)

90

c)

30

d)

120

45.

in a balanced 3-phase wye connected generator, the line-to-line voltage is

a)

equal to the phase voltage

b)

two times the phase voltage

c)

1.41 times the phase voltage

d)

1.732 times the phase voltage

46.

in a balanced three phase star connected system, the line voltage is

a)

the phasor difference of two-phase voltages

b)

the phasor sums of two phases voltages

c)

0.707 times phase voltage

d)

1.414 times phase voltage

47.

the voltage phasor of a three-phase balance voltage system is V_AB = 230cis30 deg Volts and

V_BC =230cis270 deg Volts. what is the phase sequence of the voltage system.

a)

ABC

b)

CBA

c)

BAC

d)

ACB

48.

a system consists of three equal resistors connected in delta and is fed from balanced three phase supply. the power is reduced to ___ if one of the resistors is disconnected?

a)

33%

b)

25%

c)

50%

d)

67%

49.

a balanced delta connected load has impedance Z1 = Z2 = Z3. what is per phase equivalent impedance in wye?

a)

$\frac{Z1}{3}$

b)

$\frac{2Z1}{3}$

c)

3Z1

d)

Z1

50.

in a star connected system, the line current is

a)

0.707 times the phase current

b)

equal to the phase current

c)

1.732 times the phase current

d)

1.414 times the phase current

51.

in delta connected system, the line current is

a)

phasor sum of the two-phase current

b)

equal to the phase current

c)

1.414 times phase current

d)

1.732 times the phase current

52.

in the balanced three-phase ABC system, the line voltage ___ the phase voltage and the line current ___ the phase current by 30 degrees.

a)

lags, lags

b)

lags, leads

c)

leads, leads

d)

leads, lags

53.

the phase sequence of a three-phase system is BCA. the other possible phase sequences can be ___

a)

CBA

b)

ACB

c)

CAB

d)

BAC

54.

the advantage of star connection for the same phase voltage is that it gives

a)

step down current

b)

extra step-up current

c)

extra step-up voltage

d)

extra step-up power

55.

when the phase sequence at the three-phase load is reversed

a)

phase power is changed

b)

phase current is changed

c)

phase current is changed in angle but not in magnitude

d)

total power consume is changed

56.

power in star connected system is

a)

equal to that delta system

b)

1.732 times the delta system

c)

1.414 times the delta system

d)

3 times the delta system

57.

in a three-phase supply floating neutral is undesirable because it gives way to

a)

high voltage across the load

b)

unequal line voltages across the load

c)

low voltage across the load

d)

open circuit

58.

a wattmeter is installed in a balanced 3-phase system with current coil at line A while voltage coil across B and C. the wattmeter will measure.

a)

total power

b)

active power

c)

real power

d)

reactive power

59.

what is the minimum number of wattmeter/s required for measuring power of a three-phase balanced load?

a)

two

b)

four

c)

one

d)

three

60.

in two wattmeter method, the reading of one of the watt meters will be zero when

a)

load in one of the phases is zero

b)

power factor is 0.5

c)

power factor is unity

d)

neutral is earthed

61.

two wattmeters can be used to measure 3 phase powers for a

a)

balanced and unbalanced load

b)

balanced load only

c)

unbalanced load only

d)

unity power factor only

62.

what is the minimum number of wattmeter's required to measure unbalanced power of a three-phase system?

a)

two

b)

four

c)

three

d)

one

63.

the least number of 1-phase wattmeter required to measure the total power consumed by an unbalance load fed from 3-phase 4-wire system is

a)

one

b)

three

c)

two

d)

four

64.

a 3-phase load is balanced if all three phases have the same ___.

a)

Z

b)

Z & p.f

c)

p.f

d)

P

65.

in a balanced 2-phase system, the total power is

a)

1.414 x V_L x I_L x power factor

b)

1.414 x V_L x I_N x power factor

c)

2 x V_PH x I_N x power factor

d)

2 x V_L x I_PHx power factor

66.

the power factor angle of a balanced 3-phase load is the phase angle between

a)

line voltage and line current

b)

line voltage and phase current

c)

phase voltage and line current

d)

phase voltage and phase current

67.

in a star connected system, the line current is

a)

0.707 times the phase current

b)

equal to the phase current

c)

1.732 times the phase current

d)

1.414 times the phase current

68.

in a three phase wye connected balanced load system, the angle between line current and phase current is ___ degrees.

a)

30

b)

45

c)

90

d)

0

69.

for an unbalance load, which connection is suitable

a)

3-wire open delta

b)

3-wire delta connection

c)

4-wire star connection

d)

3-wire star connection

70.

in 2-wattmeter method, the reading in one of the wattmeter will be zero when

a)

power factor is unity

b)

load in one of the phases is zero

c)

power factor is 0.5

d)

a neutral wire is not provided

71.

a wattmeter is installed in a balanced 3-phase system with current coil at line A while voltage coil across B and C. the wattmeter will measure

a)

total powr

b)

real power

c)

active power

d)

reactive power

72.

an advantage of ac over dc in utility application is:

a)

AC is safer for household appliances than DC.

b)

DC can be easily transformed to different voltage levels.

c)

AC can be easily transformed from one voltage to another

d)

AC is more efficient for long-distance transmission than DC.

73.

what figure of merit describes the ratio of the maximum value and the rms value?

a)

Peak factor

b)

Form factor

c)

Average factor

d)

Crest factor

74.

what is the term used to identify an AC voltage that would cause the same heating in a resistor as a corresponding value of DC voltage?

a)

Peak voltage

b)

Root Mean Square (RMS) voltage

c)

Average voltage

d)

Effective voltage

75.

the length of time between a point in one cycle and the same point in the next cycle of an ac wave is the:

a)

frequency

b)

amplitude

c)

period

d)

wavelength

76.

if two waves have the same frequency and the same phase, the composite wave:

a)

has a magnitude equal to the sum of the two originals

b)

has a frequency that is twice as high.

c)

has the same frequency but no amplitude

d)

has half the amplitude.

77.

what part of an alternating current is defined as a current which will produce the same heating effect as an equivalent direct current?

a)

effective value

b)

Instantaneous Current

c)

Average Current

d)

Peak Current

78.

a rotating vector is known as a/an ___.

a)

linear

b)

phasor

c)

static

d)

fixed

79.

if two waves have the same frequency and the same amplitude, but opposite phase, the composite wave is:

a)

double

b)

half

c)

two separate waves with no interaction

d)

zero

80.

Which of the following can vary with AC, but not with DC?

a)

voltage

b)

current

c)

frequency

d)

resistance

81.

the average value of a symmetrical alternating quantity, (such as a sine wave), is the average value measured over a ___ cycle.

a)

full

b)

half

c)

quarter

d)

three-quarter

82.

the period of an ac wave is:

a)

equal to the frequency

b)

equal to 1 divided by the frequency

c)

equal to the square of the frequency

d)

independent of the frequency

83.

on a spectrum analyzer, a pure ac signal, having just one frequency component, would look like:

a)

a single pip

b)

multiple pips

c)

a continuous wave

d)

a flat line

84.

as the size of the plates in a capacitor increase, all other things being equal:

a)

the value of Xc increases positively

b)

the value of Xc decreases negatively

c)

the capacitance remains constant

d)

the capacitance decreases

85.

as the frequency of a wave gets lower, all other things being equal, the value of Xc for a capacitor ___.

a)

decreases positively

b)

increases negatively

c)

remains constant

d)

becomes zero

86.

if the dielectric material between the plates of a capacitor is changed, all other things being equal:

a)

you cant say what happens to Xc without more data

b)

the value of Xc decreases negatively

c)

The capacitance increases

d)

The capacitance decreases

87.

each impedance R-jXc:

a)

represents a unique combination of resistance and reactance.

b)

represents only resistance

c)

represents only reactance

d)

represents a purely inductive impedance

88.

as the number of turns in a coil increases, the reactance ___.

a)

decreases

b)

remains constant

c)

increases

d)

becomes zero

89.

each point in the RC plane:

a)

represents only resistance

b)

represents only reactance

c)

corresponds to a unique combination of resistance and reactance.

d)

represents a purely inductive impedance

90.

in an RC circuit, as the ratio of capacitive reactance to resistance, -Xc/R, gets closer to zero, the phase angle ___.

a)

increase to near 90 degrees.

b)

decreases to near zero

c)

remains constant

d)

becomes undefined

91.

if R increases in an RC circuit, but Xc is always zero, then the vector in the RC plane will:

a)

point straight upwards

b)

point straight towards the right

c)

point diagonally upwards

d)

point diagonally downwards

92.

each point in the RL plane:

a)

represents only resistance

b)

represents only reactance

c)

corresponds to a unique combination of resistance and inductive reactance.

d)

represents a purely capacitive impedance

93.

which of the following effects are generally less for an alternating current than for a direct current?

a)

magnetic effects

b)

heating effects

c)

chemical effects

d)

mechanical effects

94.

if R increases in an RC circuit, but the capacitance and the frequency are nonzero and constant, then the vector in the RC plane will:

a)

get shorter and rotate counterclockwise

b)

get longer and rotate clockwise

c)

remain the same length and direction

d)

get shorter and rotate clockwise

95.

as the frequency of an ac wave gets lower, the value of X_L for a particular coil ___.

a)

increases

b)

decreases

c)

remains constant

d)

becomes infinite

96.

Phase sequence depends on the ________.

a)

rotation of the field

b)

rotation of the armature

c)

field

d)

armature

97.

Phase voltages of a star – connected alternator are E_R = 231/_0 V; E_Y = 231/_-120 V; and E_B = 231/_120 V. What is the phase sequence of the system?

a)

BYR

b)

RYB

c)

YRB

d)

RBY

98.

What is the percentage of power increased from single phase to three phase?

a)

50

b)

200

c)

150

d)

100

99.

If RR’, YY’ and BB’ constitutes three phase sequence if V’RR = Vmsinωt its corresponding field magnets are in clockwise direction, then V’YY =?

a)

Vm sin(ωt - 120°)

b)

Vm sinωt

c)

Vm sin(ωt - 240°)

d)

Vm sin(ωt + 120°)

100.

If a resistor Rx is connected between nodes X and Y, Ry between X and Y, Rz between Y and Z to form a delta connection, then after transformation to star, the resistance at node Y is?

a)

$\frac{RzRy}{(Rx+Ry+Rz)}$

b)

$\frac{RzRx}{(Rx+Ry+Rz)}$

c)

$\frac{(Rz+Ry)}{(Rx+Ry+Rz)\ }$

d)

$\frac{RxRy}{(Rx+Ry+Rz)\ }$

101.

If a resistor Rx is connected between nodes X and Y, Ry between X and Y, Rz between Y and Z to form a delta connection, then after transformation to star, the resistor at node X is?

a)

$\frac{(Rx+Ry)}{(Rx+Ry+Rz)}$

b)

$\frac{RzRy}{(Rx+Ry+Rz)}$

c)

$\frac{RxRy}{(Rx+Ry+Rz)}$

d)

$\frac{RxRz}{(Rx+Ry+Rz)}$

102.

If the resistors of star connected system are R₁, R2, R3 then the resistance between 2 and 3 in delta connected system will be?

a)

$\frac{(R₁R₂+R₂R₃+R₃R₁)}{(R₃+R₂)}$

b)

$\frac{(R₁R₂+R₂R₃+R₃R₁)}{R₃}$

c)

$\frac{(R₁R₂+R₂R₃+R₃R₁)}{R₁}$

d)

$\frac{(R₁R₂+R₂R₃+R₃R₁)}{R₂}$

103.

If a star connected system has equal impedances Z₁, then after converting into delta connected system having equal impedances Z₂, then?

a)

Z₂ = 2Z₁

b)

Z₂ = 3Z₁

c)

Z₂ = Z₁

d)

Z₂ = 4Z₁

104.

The power generated by a machine increases _____ percent from single phase to two phase.

a)

40.4

b)

42.4

c)

41.4

d)

43.4

105.

In a two-phase generator, the armature has two distinct windings that are displaced ________ apart.

a)

180°

b)

135°

c)

90°

d)

45°

106.

In three phase system at any given instant, the algebraic sum of three voltages must be?

a)

1

b)

0

c)

3

d)

2

107.

If the resistors of star connected system are R₁, R₂, R₃ then the resistance between 1 and 2 in delta connected system will be?

a)

$\frac{(R₁R₂+R₂R₃+R₃R₁)}{(R₁+R₂)}$

b)

$\frac{(R₁R₂+R₂R₃+R₃R₁)}{R₁}$

c)

$\frac{(R₁R₂+R₂R₃+R₃R₁)}{R₂}$

d)

$\frac{(R₁R₂+R₂R₃+R₃R₁)}{R₃}$

108.

If the resistors of star connected system are R₁, R2, R3 then the resistance between 3 and 1 in delta connected system will be?

a)

$\frac{(R₁R₂+R₂R₃+R₃R₁)}{R₃}$

b)

$\frac{(R₁R₂+R₂R₃+R₃R₁)}{(R₃+R₁)}$

c)

$\frac{(R₁R₂+R₂R₃+R₃R₁)}{R₂}$

d)

$\frac{(R₁R₂+R₂R₃+R₃R₁)}{R₁}$

109.

If the load impedance is $Z\angleφ$ What is the expression obtained for current ( $I_y$ )?

a)

$\left(\frac{V}{Z}\right)\angle120+φ$

b)

$\left(\frac{V}{Z}\right)\angle-120+φ$

c)

$\left(\frac{V}{Z}\right)\angle-120-φ$

d)

$\left(\frac{V}{Z}\right)\angle120-φ$

110.

In a delta-connected load, what is the relation between line voltage and the phase voltage?

a)

Line voltage > phase voltage

b)

Line voltage < phase voltage

c)

Line voltage = phase voltage

d)

Line voltage ≥ phase voltage

111.

If the load impedance is $Z\angleφ$ , then the current ( $I_R$ ) is __.

a)

$\left(\frac{V}{Z}\right)\angle90-φ$

b)

$\left(\frac{V}{Z}\right)\angle-φ$

c)

$\left(\frac{V}{Z}\right)\angle-90+φ$

d)

$\left(\frac{V}{Z}\right)\angleφ$

112.

If the load impedance is $Z\angleφ$ , then what is the expression obtained for current ( $I_B$ )?

a)

$\left(\frac{V}{Z}\right)\angle-240+φ$

b)

$\left(\frac{V}{Z}\right)\angle-240-φ$

c)

$\left(\frac{V}{Z}\right)\angle240+φ$

d)

$\left(\frac{V}{Z}\right)\angle240-φ$

113.

Polyphase generators produce simultaneous multiple sinusoidal voltages that are separated by

a)

Certain constant currents

b)

Certain constant voltages

c)

Certain constant frequencies

d)

Certain constant phase angles

114.

If the system is a three-wire system, the currents flowing towards the load in the three lines must add to _ at any given instant.

a)

three

b)

zero

c)

two

d)

one

115.

Power is measured in a three-phase load by using an ammeter.

a)

Neither True or False

b)

True

c)

Either True or False

d)

False

116.

In a Y-connected circuit, the magnitude of each line current is ___.

a)

equal to the corresponding phase current

b)

zero

c)

one-third the phase current

d)

three times the corresponding phase current

117.

Polyphase is characterized by two or more sinusoidal voltages, each having a different phase angle.

a)

Neither True of False

b)

True

c)

Either True or False

d)

False

118.

Long distance railways use which of the following?

a)

25 kV two phase ac

b)

25 kV three phase ac

c)

25 kV single phase ac

d)

200 V dc

119.

In a balanced three-phase load, each phase has __.

a)

one-third of total power

b)

a power consumption equal to $\sqrt[]{3}\times V_L\times I_L$

c)

two-thirds of total power

d)

an equal amount of power

120.

In a Y-connected generator, there is a 120° difference between each line voltage and the nearest phase voltage.

a)

Neither True or False

b)

Either True or False

c)

True

d)

False

AC CIRCUITS OBJECTIVES

Total questions: 120

Worksheet time: 3600secs

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