The best material for the core of a transformer is
stainless steel
soft iron
hard steel
mild steel
Quantity that remains unchanged in a transformer is
voltage
current
frequency
none of these
A transformer is having 2100 turns in the primary and 4200 turns in the secondary. An a.c. source 120 V, 10 A is connected to the primary. The secondary voltage and current are :
120 V, 10 A
240 V, 10 A
120 V, 20 A
240 V, 5 A
The primary winding of a transformer has 500 turns whereas its secondary has 5000 turns. The primary is connected to an a.c. supply of 20 V, 50 Hz. The secondary will have an output of
2 V, 50 Hz
200 V, 50 Hz
200 V, 500 Hz
2 V, 5 Hz
The magnetic effect of current was discovered by
Maxwell
Fleming
Oersted
Faraday
Iron core is used in a transformer to
provide tight magnetic coupling
increase the weight
reduce copper losses
increase copper losses
A transformer is used to reduce the mains supply of 220 V to 11 V. If currents in the primary and secondary are 5 A and 90 A respectively, efficiency of the transformer is
75%
60%
40%
90%
In a transformer, the number of turns of primary coil and secondary coil are 5 and 4 respectively. If 240 V is applied on the primary, then the ratio of currents in the primary and secondary coil is
4 : 5
5 : 4
1 : 3
3 : 1
A transformer of 100% efficiency has 500 turns in the primary and 10,000 turns in the secondary. If the primary is connected to 220 V mains supply, what is the voltage across the secondary?
2500 V
4000 V
3500 V
4400 V
In a noiseless transformer, an alternating current of 2 A is flowing in the primary. The number of turns in the primary and secondary coils are 100 and 20 respectively. The value of current in the secondary is
0.08 A
0.4 A
5 A
10 A
