﻿ If voltage across a bulb rated 220 V -100W drops by 2.5% of its rated value, the percentage of the rated value by which the power would decrease is | Alternating Current

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# Alternating Current

#### Multiple Choice Questions

1.

A resistance 'R' draws power 'P' when connected to an AC source. If an inductance is now placed in series with the resistance such that the impedance of the circuit becomes 'Z' the power drawn will be

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2.

A small signal voltage V(t) = Vo sin  is applied across an ideal capacitor C:

• over a full cycle the capacitor C does not consume any energy from the voltage source

• current I(t) is in phase with voltage V(t)

• Current I(t) leads voltage V(t) by 180o

• Current I(t) leads voltage V(t) by 180o

1685 Views

3.

An inductor of 20 mH, a capacitor of 50  and a resistor of 40 ohm are connected in series across a source of emf V = 10 sin 340 t. the power loss in the ac circuit is,

• 0.67 W

• 0.76 W

• 0.89 W

• 0.89 W

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4.

The instantaneous values of alternating current and voltages in a circuit are given as

The average power in Watts consumed in the circuit is

• 1/4

• 1/2

• 1/2

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# 5.If voltage across a bulb rated 220 V -100W drops by 2.5% of its rated value, the percentage of the rated value by which the power would decrease is 20% 2.5% 5% 5%

C.

5%

Power P= V2/R
For small variation

ΔP/P x 100%

Therefore, power would decrease by 5%

552 Views

6.

A transformer having efficiency of 90% is working on 200 V and 3 kW power supply. If the current in the secondary coil is 6 A, the voltage across the secondary coil and the current in the primary coil respectively are:

• 300 V, 15 A

• 450 V, 15 A

• 450 V, 13.5 A

• 450 V, 13.5 A

895 Views

7.

In an AC circuit, an alternating voltage 100t volt is connected to a capacitor of capacity 1μF. The rms value of the current in the circuit is

• 100 mA

• 200 mA

• 20 mA

• 20 mA

378 Views

8.

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 3Ω, the phase difference between the applied voltage and the current in the circuit is

• π/4

• π/2

• zero

• zero

714 Views

9.

In the given figure, a diode D is connected to an external resistance R = 100 Ω and an e. m. f of 3.5 V. If the barrier potential developed across the diode is 0.5 V, the current in the circuit will be

• 30 mA

• 40 mA

• 20 mA

• 20 mA

947 Views

10.

The rms value of potential difference V shown in the figure is

• Vo

• Vo/2

• Vo/2

880 Views