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
A step-up transformer operates on 230 V line and supplies a load of 2 A. The ratio of primary and secondary turns is 1 : 25. The current in the primary is
50 A
25 A
15 A
12.5 A
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%
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
A transformer will work on
d.c. only
a.c. only
a.c. as well as d.c.
none of the above
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
Quantity that remains unchanged in a transformer is
voltage
current
frequency
none of these
A transformer is an efficient device because it
uses inductive coupling
is a static device
uses electric coupling
uses capacitive coupling
The best material for the core of a transformer is
stainless steel
soft iron
hard steel
mild steel
A step-up transformer is used on a 120 V line to provide a potential difference of 2400 V. If the primary coil has 75 turns, the number of turns in the secondary coil is
150
1200
1500
1575