A transformer is used to light a `100 W` and `110 V` lamp from a `220V` mains. If the main current is `0.5 A`, the efficiency of the transformer is approximately:

Options

A. `30%`
B. `50%`
C. `90%`
D. `10%`

Answer

C

Explanation

`eta=P_("out")/P_("in")=100/(220xx0.5)xx100=90.9%~~90%`.