15 Questions

Time: 30 Minute

Questions and Answers

- 1.If the rms current in a 50 Hz ac circuit is 5 A, the value of the current 1/300 seconds after its value becomes zero is
- A.
- B.
- C.
- D.

- 2.To reduce the reasonant frequency in an LCR series circuit with a generator
- A.
The generator frequency should be reduced

- B.
Another capacitor should be added in parallel to the first

- C.
The iron core of the inductor should be removed

- D.
Dielectric in the capacitor should be removed

- 3.An inductor of reactance 1 Ω and a resistor of 2 Ω are connected in series to the terminals of a 6 V (rms) a.c. source. The power dissipated in the circuit is
- A.
8 W

- B.
12 W

- C.
14.4 W

- D.
18 W

- 4.The natural frequency of an LC circuit is 1, 25, 000 c/s. Then the capacitor C is replaced by another capacitor with a dielectric medium of constant K. In this case, the frequency decreases by 25 kHz. The value of K is
- A.
1.56

- B.
2.1

- C.
3

- D.
1.7

- 5.In the given circuit: The reading of voltmeter V
_{1}and V_{2}are 300 volts each. The reading of the voltmeter V_{3}and ammeter A are respectively- A.
150 V, 2.2 A

- B.
220 V, 2.2 A

- C.
220 V, 2.0 A

- D.
100 V, 2.0 A

- 6.In the circuit: What is the energy stored in the coil at steady state?
- A.
21.3 J

- B.
42.6 J

- C.
Zero

- D.
213 J

- 7.
- A.
50 W

- B.
100 W

- C.
200 W

- D.
400 W

- 8.A pure resistive circuit element X when connected to an ac supply of peak voltage 200 V gives a peak current of 5 A which is in phase with the voltage. A second circuit element Y, when connected to the same AC supply also gives the same value of peak current but the current lags behind by 90
^{ o}. If the series combination of X and Y is connected to the same supply, what will be the rms value of current?- A.
- B.
- C.
- D.

- 9.For the LR circuit: The phase angle if frequency is 100/π is
- A.
30

^{o} - B.
60

^{ o} - C.
45

^{ o} - D.
90

^{ o}

- 10.An AC voltage source of variable angular frequency ω and fixed amplitude V
_{0}is connected in series with a capacitance C and an electric bulb of resistance R (inductance zero). When ω is increased- A.
The bulb glows dimmer

- B.
The bulb glows brighter

- C.
Total impedance of the circuit is unchanged

- D.
Total impedance of the circuit increases

- 11.In a series LCR circuit R = 200 Ω and the voltage and the frequency of the main supply is 220 V and 50 Hz respectively. On taking out the capacitance from the circuit, the current lags behind the voltage by 30
^{o}. On taking out the inductor from the circuit, the current leads the voltage by 30^{o}. The power dissipated in the LCR circuit is- A.
210 W

- B.
Zero W

- C.
242 W

- D.
305 W

- 12.An ac voltage is applied to a resistance R and an inductor L in series. If R and the inductive reactance are both equal to 3 Ω, the phase difference between the applied voltage and the current in the circuit is
- A.
Ï€/6

- B.
Ï€/4

- C.
Ï€/2

- D.
Zero

- 13.If an electrical circuit R, L, C and an a.c. voltage source are all connected in series. When L is removed from the circuit, the phase difference between the voltage and the current in the circuit is π/3. If instead, C is removed from the circuit, the phase difference is again π/3. The power factor of the circuit is:
- A.
- B.
- C.
- D.

- 14.An LCR series circuit is connected to a source of alternating current. At resonance, the applied voltage and the current flowing through the circuit will have a phase difference of
- A.
Ï€

- B.
Ï€/2

- C.
Ï€/4

- D.
0

- 15.The electrical energy spent in running the circuit for one hour is
- A.
20.05 J

- B.
20.05 k w h

- C.
7.22 x 104 J

- D.
Zero