﻿ In an AC circuit, the emf (e) and the current (i) at any instant are given respectively bye = E0 sin ωti = Io sin (ωt -Φ)The average power in the circuit over one cycle of AC is | Alternating Current

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# Alternating Current

#### Multiple Choice Questions

11.

A 220 V input is supplied to a transformer. The output circuit draws a current 2.0 A at 440 V. If the efficiency of the transformer is 80%, the current drawn by the primary windings of the transformer is

• 3.6 A

• 2.8 A

• 2.5 A

• 2.5 A

369 Views

12.

The two ends f a rod of length L and a uniform cross -sectional area A are kept at two temperatures T1 and T2 (T2 > T1) .The rate of heat transfer, dQ/dt, through the rod in steady state is given by

452 Views

13.

A galvanometer having a coil resistance of 60 Ω shows full-scale deflection when a current of 1.0 A passes through it. It can be converted into an ammeter to read currents up to 5.0 A by

• putting in parallel a resistance of 240 Ω

• putting in series a resistance of 15 Ω

• putting in series a resistance of 240 Ω

• putting in series a resistance of 240 Ω

581 Views

# 14.In an AC circuit, the emf (e) and the current (i) at any instant are given respectively bye = E0 sin ωti = Io sin (ωt -Φ)The average power in the circuit over one cycle of AC is

C.

The power is defined as the rate at which work is being done in the circuit.
Power = rate of work done in one complete cycle.
Or
Pav = W/T

where cos Φ is called the power factor of an AC circuit.

425 Views

15.

In the circuit shown, the current through the 4 Ω resistor is 1 A when the points P and M are connected to a DC voltage source. The potential difference between the point M and N is

• 1.5 V

• 1.0 V

• 0.5 V

• 0.5 V

454 Views

16.

The primary and secondary coil of a transformer have 50 and 1500 turns respectively. If the magnetic flux Φ linked with the primary coil is given Φ = Φo +4t, where Φ is in weber, t is time is second and Φo is a constant the output voltage across the secondary coil is:

• 90 V

• 120 V

• 220 V

• 220 V

867 Views

17.

A charged particle (charge q ) is moving n a circle of radius R with uniform speed v. The associated magnetic moment μ is given by:

• qvR/2

• qVR2

• qVR2/2

• qVR2/2

2058 Views

18.

A common emitter amplifier has a voltage gain of 50, an input impedance of 100 Ω and an output impedance of 200 Ω. The power gain of the amplifier is:

• 500

• 1000

• 1250

• 1250

687 Views

19.

The core of a transformer is laminated because

• energy losses due to eddy currents may be minimised

• the weight of the transformer may be reduced

• rusting of the core may be prevented

• rusting of the core may be prevented

473 Views

20.

A coil of inductive reactance 31 Ω has a resistance of 8Ω. It is placed in series with a condenser of capacitative reactance 25Ω. The combination is connected to an a.c. soruce of 110 V. The power factor of the circuit is

• 0.56

• 0.64

• 0.80

• 0.80

500 Views