﻿ 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 | 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 by

e = E0 sin ωt
i = Io sin (ωt -Φ)

The average power in the circuit over one cycle of AC is

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

C.

0.80

Power factor  is the ratio of resistance and impedance of a.c. circuit.
Power factor of a.c. circuit is given by
...(i)
where R is resistance employed and z the impedance of the circuit.
...(ii)
Eqs. (i) and (ii) meet to give,
...(iii)
Given,

500 Views