Question

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?

(a) Both A and R are true and R is the correct explanation of A

(b) Both A and R are true but R is not a correct explanation of A

(c) A is true but R is false

(d) A is false but R is true

Answer 1

(c) A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors–the transformer' coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer' core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a voltage in the secondary winding. By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) or voltage to be "stepped up" by making Ns greater than Np or "stepped down" by making Ns less than Np. Here Np represents number of turns in primary winding. Ns represents the number of turns in secondary winding. As it is clear from principle involved that transformer can be used to step up and step down A.C. voltage only. This device can not be used for D.C. voltage as its working is based on the change of magnetic flux with varying current.