Alternating Current

A series L.R circuit connected with an ac source E=(25 1000t) V has a power factor of 1 2. If the source of emf is changed to E=(20 2000t) V, the new power factor of the circuit will be :

1. 1 3
2. 1 2
3. 1 5
4. 1 7

An alternating voltage V(t)=220 100 t volt is applied to a purely resistive load of 50 . The time taken for the current to rise from half of the peak value to the peak value is:

1. 7.2 ms
2. 3.3 ms
3. 5 ms
4. 2.2 ms

A power transmission line feeds input power at 2.3 kV to a step down transformer with its primary winding having 3000 turns. The output power is delivered at 230 V by the transformer. The current in the primary of the transformer is 5 A and its efficiency is 90\%. The winding of transformer is made of copper. The output current of transformer is A.

A capacitor of capacitance 100 is charged to a potential of 12 V and connected to a 6.4 mH inductor to produce oscillations. The maximum current in the circuit would be :

1. 2.0 A
2. 3.2 A
3. 1.5 A
4. 1.2 A

In an a.c. circuit, voltage and current are given by: V=100 (100t) V and I=100 (100t+ 3 )mA respectively. The average power dissipated in one cycle is:

1. 5 W
2. 25 W
3. 2.5 W
4. 10 W

Primary side of a transformer is connected to 230 V, 50 Hz supply. Turns ratio of primary to secondary winding is 10:1. Load resistance connected to secondary side is 46 . The power consumed in it is :

1. 11.5 W
2. 12.5 W
3. 10.0 W
4. 12.0 W

A series LCR circuit with L= 100 mH, C= 10-3 F and R=10 , is connected across an ac source of 220 V, 50 Hz supply. The power factor of the circuit would be .