Alternating Current

In an ac circuit, the instantaneous current is zero, when the instantaneous voltage is maximum. In this case, the source may be connected to : Choose the correct answer from the options given below :

1. A, B and C only
2. A and B only
3. A, B and D only
4. B, C and D only

An alternating current at any instant is given by i= [6+ 56 (100 t+ /3) ] A. The rms value of the current is A.

Match List I with List II Choose the correct answer from the options given below:

1. A-IV, B-I, C-III, D-II
2. A-I, B-IV, C-II, D-III
3. A-IV, B-I, C-II, D-III
4. A-I, B-IV, C-III, D-II

In series LCR circuit, the capacitance is changed from C to 4C. To keep the resonance frequency unchanged, the new inductance should be:

1. increased by 2 L
2. reduced by 14 L
3. reduced by 34 L
4. increased to 4 L

A transformer has an efficiency of 80\% and works at 10 V and 4 kW. If the secondary voltage is 240 V, then the current in the secondary coil is :

1. 1.33 A
2. 13.33 A
3. 1.59 A
4. 15.1 A

An AC voltage V=20 200 t is applied to a series LCR circuit which drives a current I=10 (200 t+ 3 ). The average power dissipated is:

1. 21.6 W
2. 200 W
3. 173.2 W
4. 50 W

Primary coil of a transformer is connected to 220 V ac. Primary and secondary turns of the transformer are 100 and 10 respectively. Secondary coil of transformer is connected to two series resistances shown in figure. The output voltage (V0) is : [figure]

1. 7 V
2. 44 V
3. 22 V
4. 15 V

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.