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Alternating Current

Multiple Choice Questions

1.

A transmitting station transmits radiowaves of wavelength 360 m. Calculate the inductance of coil required with a condenser of capacity 1.20 μF in the resonant circuit to receive them

• 3.07×10-8 H

• 2.07×10-8 H

• 4.07×10-8 H

• 6.07×10-8 H

2.

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

3.

The core used in transformer and other electromagnetic instruments is laminated, the reason is

• to increase the electric field

• to increase the magnetic field

• to reduce the loss of energy due to eddy currents

• to decrease the resistance

4.

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

• resistor circuit

• capacitor

• inductor circuit

• CR circuit

5.

The peak value of alternating current is $5\sqrt{2}$ ampere. The mean square value of current will be

• 5 A

• 2.5 A

• $5\sqrt{2}$ A

• None of the above

6.

An AC supply gives 30Vrms which is fed on a pure resistance of 10 ohm. the power dissipated in this is

• 90watt

• 45watt

• 90.2watt

• 180watt

7.

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.

8.

A capacitor when charged by a potential difference of 200 volt, stores a charge of 0.1 C. By discharging, energy liberated by the capacitor is

• -30 J

• -15 J

• 10 J

• 20 J

9.

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

10.

A coil having resistance of 50 ohm and an inductance of 10 ohm, is connected to a 100 volt battery. The energy stored in the coil is

• 10 J

• 20 J

• 30 J

• 40 J