Topic AC - Alternating Current Set 1, Physics MCQ Quiz Test

MCQ 1:
In an A.C. circuit capacitance of 5μF has a reactance as 1/1000 Ω. The frequency of A.C. in MHz will be -

1000/π
100/π
200
5000

MCQ 2:
In an A.C. circuit X_L = 300Ω, X_C = 200Ω and R = 100Ω the impedance of circuit is -

600 Ω
200 Ω
141 Ω
None of the above

MCQ 3:
A resistance of 50Ω, an inductance of 20/π Henry and a capacitor of 5/π μF are connected in series with an A.C. source of 230 volt and 50 Hz. The impedance of circuit is -

5 Ω
50 Ω
5K Ω
500 Ω

MCQ 4:
In an L–C–R series circuit R = √5 Ω, X_L = 9Ω and X_C = 7Ω. If applied voltage in the circuit is 50 volt then impedance of the circuit in ohm then impedance of the circuit in ohm will be -

2
3
2√5
3√5

MCQ 5:
The potential difference between the ends of a resistance R is V_R between the ends of capacitor is V_C = 2V_R and between the ends of inductance is V_L = 3V_R, then the alternating potential of the source in terms of V_R will be -

√2 V_R
V_R
V_R/√2
5V_R

MCQ 6:
In an A.C. circuit the impedance is Z = 100 ∠30° Ω, then the resistance of the circuit in ohm will be -

50
100
50√3
100√3

MCQ 7:
In an LCR circuit, the voltages across the components are V_L, V_C and V_R respectively. The voltage of source will be -

[ V_R + V_L + V_C ]
[ V_R² + V_L² + V_C² ]^1/2
[ V_R² + ( V_L + V_C )² ]^1/2
[ V_R² + ( V_L – V_C )² ]^1/2

MCQ 8:
In an electric circuit the applied alternating emf is given by E = 100 sin (314 t) volt, and current flowing I = sin (314t + π/3). Then the impedance of the circuit is (in ohm) -

100 /√2
100
100√2
None of the above

MCQ 9:
The percentage increase in the impedance of an ac circuit, when its power factor changes form 0.866 to 0.5 is (Resistance constant) -

73.2%
86.6%
90.8%
66.6%

MCQ 10:
The impedance of the given circuit will be -

50 ohm
250 ohm
200 ohm
250 ohm

MCQ 11:
The impedance of the given circuit will be -

Zero
Infinite
55 ohm
2500 ohm

MCQ 12:
If E₀ = 200 volt, R = 25 ohm, L = 0.1 H and C = 10^-5 F and the frequency is variable, then the current at f = 0 and f = ∞ will be respectively -

0 A , 8 A
8 A , 0 A
8 A , 8 A
0 A , 0 A

MCQ 13:
The impedance of the circuit given will be -

Zero
Infinite
110 ohm
90 ohm

MCQ 14:
A coil of resistance R and inductance L is connected to a cell of emf E volt. The current flowing through the coil will be -

E/R
E/L

MCQ 15:
In a certain circuit E = 200 cos (314t) and I = sin (314t + π/4). Their vector representation is -

MCQ 16:
In a certain circuit E = 200 cos (314t) and I = sin (314t + π/4), the reactance X will be -

70.7 ohm
0.707 ohm
100 ohm
141 ohm

MCQ 17:
In a certain circuit E = 200 cos (314t) and I = sin (314t + π/4), the power factor is -

0.5
0.707
0.85
1.0

MCQ 18:
The electric resonance is sharp in L-C-R circuit if in the circuit -

R is greater
R is smaller
R = X_L or X_C
Does not depend on R

MCQ 19:
In a series resonant L–C–R circuit, if L is increased by 25% and C is decreased by 20%, then the resonant frequency will -

Increase by 10%
Decrease by 10%
Remain unchanged
Increase by 2.5%

MCQ 20:
If R = 100 Ω then the value of X and I in the given circuit will be -

800 V, 2A
300 V, 2A
220 V, 2.2A
100 V, 2A

MCQ 21:
If R = 100 Ω, the value of inductance will be -

0.12 H
0.24 H
0.31 H
0.43 H

MCQ 22:
In an LCR. series circuit the resonating frequency can be decreased by -

Decreasing the value of C
Decreasing the value of L
Decreasing both the values of L and C
Increasing the value of C

MCQ 23:
Which of the following statements is correct for L–C–R series combination in the condition of resonance -

Resistance is zero
Impedance is zero
Reactance is zero
Resistance, impedance and reactance all are zero

MCQ 24:
In an LCR circuit, the resonating frequency is 500 kHz. If the value of L is increased two times and value of C is decreased 1/8 times, then the new resonating frequency in kHz will be -

250
500
1000
2000

MCQ 25:
In resonating circuit value of inductance and capacitance is 0.1H and 200 μF. For same resonating frequency if value of inductance is 100H then necessary value of capacitance in μF will be -

4
0.2
2
0.3

MCQ 26:
The inductance of the motor of a fan is 1.0 H. To run the fan at 50 Hz the capacitance of the capacitor that will cancel its inductive reactance, will be -

10 μF
40 μF
0.4 μF
0.04 μF

MCQ 27:
In ac circuit at resonance -

Impedance = R
Impedance = (ωL – 1/ωC)
The voltages across L and C are in the same phase
The phase difference of current in C relative to source voltage is π

MCQ 28:
An ac circuit resonates at a frequency of 10 kHz. If its frequency is increased to 11 kHz, then -

Impedance will increase by 1.1 times
Impedance will remain unchanged
Impedance will increase and become inductive
Impedance will increase and become capacitive

MCQ 29:
?n an ac circuit 6 ohm resistor, an inductor of 4 ohm and a capacitor of 12 ohm are connected n series with an ac source of 100 volt (rms). The average power dissipated in the circuit will be -

600 W
500 W
400 W
200 W

MCQ 30:
In an ac circuit emf and current are E = 5 cos ωt volt and I = 2 sin ωt ampere respectively. The average power dissipated in this circuit will be -

10 W
2.5 W
5 W
Zero

MCQ 31:
The equations of alternating e.m.f. and current in an A.C. circuit are E = 5 cos ωt volt and I = 2 sin (ωt + π/6) ampere respectively. The average power loss in this circuit will be -

1 watt
2.5 watt
3 watt
Zero

MCQ 32:
The series combination of resistance R and inductance L is connected to an alternating source of e.m.f. e = 311 sin (100 πt). If the value of wattless current is 0.5A and the impedance of the circuit is 311?????, the power factor will be -

1/2
1/√2
1/√3
1/√5

MCQ 33:
In an L–C–R series circuit the loss of power is in -

Only R
Only L
Only C
Both L and C

MCQ 34:
In an ac circuit the readings of an ammeter and a voltmeter are 10 A and 25 volt respectively, the power in the circuit will be -

More than 250 W
Always less than 250 W
250 W
Less than 250 W or 250 W

MCQ 35:
A choke coil of 100 ohm and 1 H is connected to a generator of E = 200 sin (100t) volt. The average power dissipated will be -

Zero
200 W
141 W
100 W

MCQ 36:
A choke coil of negligible resistance carries 5 mA current when it is operated at 220 V. The loss of power in the choke coil is -

Zero
11 W
44 × 10³ W
1.1 W

MCQ 37:
The ratio of apparent power and average power in an A.C. circuit is equal to –

Reciprocal of power factor
Efficiency
Power factor
Form factor

MCQ 38:
In an A.C. circuit, a resistance of 3 Ω, an inductance coil of 4 Ω and a condenser of 8 Ω are connected in series with an A.C. source of 50 volt (R.M.S.). The average power loss in the circuit will be -

600 watt
500 watt
400 watt
300 watt

MCQ 39:
In an A.C. circuit, i = 5 sin (100t – π/2) ampere an A,V, V = 200 sin (100 t) volt. The power loss in the circuit will be -

20 volt
40 volt
1000 watt
0 watt

MCQ 40:
When N identical bulbs are connected in parallel, total power consumption is P, what would be the power consumption when they connected in series-

P
PN
P/N
P/N²

MCQ 41:
Two bulbs of 500 watt and 300 watt work on 200 volt r.m.s. the ratio of their resistances will be -

25 : 9
3 : 5
9 : 25
5 : 9

MCQ 42:
An air core coil and an electric bulb are connected in series with an A.C. source. If an iron rod is put in the coil, then the intensity of bulb's will-

Be same
Increase
Decrease
Decrease, Increase

MCQ 43:
If a bulb and a coil are connected in series with D.C. source and a iron core put in the coil then the glowing of bulb -

Decreases
Increases
No change
Zero

MCQ 44:
Three bulbs of 40, 60 and 100 watt are connected in series with the source of 200 volt. Then which of the bulb will be glowing the most -

100 watt
60 watt
40 watt
All are glowing equally

MCQ 45:
If two bulbs each of 220V, 30 watt are connected in series, then we get electric power as -

60 watt
15 watt
6 watt
30 watt

MCQ 46:
Two electric bulbs of 100 watt (220 volt) are connected in series and these are connected with other bulb of 100W (220V) in parallel then total power in watt will be -

300 watt
50 watt
150 watt
25 watt

MCQ 47:
The A.C. meters are based on the principle of -

Heating effect
Magnetic effect
Chemical effect
Electromagnetic effect

MCQ 48:
The correctly marked ammeter for A.C. current is shown in -

None of these

MCQ 49:
Alternating current can not be measured by direct current meters, because -

alternating current can not pass through an ammeter
the average value of current for complete cycle is zero
some amount of alternating current is destroyed in the ammeter
None of these

MCQ 50:
The A.C. meters measure its -

root mean square value
peak value
square mean value
None of the above