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. 0.3
B. 0.5
C. 0.9
D. 0.1

Answer

C

Explanation

The efficiency of transformer
`=("Energy obtained from the secondary coil")/("Energy given to the primary coil")`
or `eta=("Out power")/("Input powr")` or `eta=(V_(S)I_(S))/(V_(p)I_(p))`
Given, `V_(S)I_(S)=100W,V_(p)=220V,I_(P)=0.5A`
Hence, `eta=(100)/(220xx0.5)=0.90=90%`