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 and secondary of a transformer are
electrically coupled
capacitively coupled
magnetically coupled
none of these
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%
Quantity that remains unchanged in a transformer is
voltage
current
frequency
Given below are two statements, one labelled as Assertion (A) and the other labelled as Reason (R)
Assertion (A) : Transformer is useful for stepping up or stepping down voltages.
Reason (R) : Transformer is a device used in D.C. circuits.
In the context of the above two statements, which one of the following is correct?
Both A and R are true and R is the correct explanation of A
Both A and R are true but R is not a correct explanation of A
A is true but R is false
A is false but R is true
The best material for the core of a transformer is
stainless steel
soft iron
hard steel
mild steel
A low-loss transformer has 230 V applied to the primary and gives 4.6 V in the secondary. Secondary is connected to a load which draws 5 A of current. The current in the primary is
0.1 A
1 A
10 A
250 A
The unit of self inductance is
henry
weber/m2
siemens
ampere-turn per weber
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
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
