A step-down transformer is employed to reduce the main supply of AC from 220V to 11V. If the primary coil draws a current of 5A and the secondary supplies a current of 90A, then the efficiency of the transformer is -
1. 10%
2. 95%
3. 90%
4. 80%
At resonance, the value of the power factor of the circuit is -
1. 1
2. Zero
3. Between zero and 1
4. More than 1
In a LCR circuit having L = 8.0 henry, C = 0.5 and R = 100 in series, the resonance frequency (in Hz) is
1.
2.
3.
4.
In a LCR series network, . The supply voltage is
1. 25V
2. 75V
3. 35V
4. Zero
The ratio of the number of turns in secondary to primary in an ideal transformer varies from 50 to 550. If the power input is P, then its output power is -
1. 11P
2.
3.
4. P
Loss in energy in the transformer is due to
1. Hysteresis
2. Eddy current loss
3. Leakage of flux
4. All of these
In a step-up transformer, the turn ratio is 1:2. A Leclanche cell (e.m.f. 1.5V) is connected across the primary coil. The voltage developed in the secondary coil would be-
1. 3.0 V
2. 0.75 V
3. 1.5 V
4. Zero
A 220 V, 50 Hz ac source is connected to an inductance of 0.2 H and a resistance of 20 ohms in series. What is the current in the circuit :
1. 10A
2. 5A
3. 33.3A
4. 3.33A
Two coils have a mutual inductance of 5 mH. Current changes in the first coil according to the equation I = cos wt, where = 10 A and rad/s. Maximum value of e.m.f. induced in the second coil is
1. 5 volt
2. 2 volt
3. 4 volt
4. volt