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Alternating Current

Multiple Choice Questions

161.

Assertion: No power loss associated with pure capacitor in ac circuit.

Reason: No current is flowing in this circuit.

If both assertion and reason are true and reason is the correct explanation of assertion
If both assertion and reason are true but reason is not the correct explanation of assertion
If assertion is true but reason is false
If both assertion and reason are false

162.

A 50 Hz a.c source of 20 volts is connected across R and C as shown in figure. The volage across R is 12 volt. The voltage across C is

8 V
16 V
10 V
not possible to determine unless values of R and C are given

163.

The circuit shown in the figure acts as

tuned filter
low pass filter
high pass filter
rectifier

164.

If an ideal parallel LC circuit, the capacitor is changed by connecting it to a d.c source which is then disconnected. The current in the circuit

becomes zero instantaneously
grows monotonically
decays monotonically
oscillates instantaneously

165.

A capacitor of capacitance 2μF is connected in the tank circuit of an oscillator oscillating with a frequency of 1 kHz. If the current flowing in the circuit is 2 mA, the voltage across the capacitor will be

0.16 V
0.32 V
79.5 V
159 V

166.

Assertion: The quantity L/R possesses dimension of time.

Reason: To reduce the rate of increase of current through a solenoid, we should increase the time constant ( L/R ).

If both the assertion and reason are true and reason is a correct explanation of assertion
If both assertion and reason are true but assertion is not correct explanation of the assertion
If the assertion is true but the reason is false.
If both assertion and reason are false.

167.
If in a circuit current lags behind EMF by $\frac{π}{2}$ . Then it is a/an

resistor circuit

capacitor

inductor circuit

CR circuit

inductor circuit

Figure shows a purely inductive circuit, in which a sinusoidal emf is applied. The induced emf across the inductor is $- L \frac{di}{dt}$ so that from Kirchoff's law.

ε_o sinωt $-$ L $\frac{di}{dt}$ = 0

⇒ $\frac{di}{dt}$ = $\frac{ε_{o}}{L}$ sinωt

⇒ i = $\frac{ε_{o}}{ω L} cosωt$ + C

The constant C can be shown to be zero from the fact that, the emf being sinusoidal, the current should also be so, and the average current over one time period has to be zero.

∴ i = $\frac{ε_{o}}{ω L}$ sin $(ωt - \frac{π}{2})$

which shows that the current lags behind the emf by a phase of $\frac{π}{2}$ .

168.

The inductance of a coil in which a current of 0.2 A is increasing at the rate of 0.5 A/s represents a power flow of 0.5 W, is

2 H
5 H
10 H
20 H

169.

In a LCR series circuit, the potential difference between the terminals of the inductance is 60 V, between the terminals of the capacitor, is 30 V and that across the resistance is 40 V. Then, the supply voltage will be equal to