# Transformers

### Explanation of question 4

In Fig. 11.1, the primary and secondary currents will be, respectively

1. 0.2A, 4A
2. 4A, 0.2A
3. 4A, 80A
4. 80A, 4A

The answer is :- 1

Power will be the same on both sides of the transformer. Therefore, if the voltage on the secondary is 20 times smaller than that on the primary, the secondary current will be 20 times larger than the primary current.

Secondary voltage = 240/20 = 12V. The secondary current, by Ohm's law I = V/R = 12/3 = 4A. Therefore the primary current will be one twentieth of this, 4/20 = 0.2A.

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