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

The efficiency of transformer
`=("Energy obtained from the secondary coil")/("Energy given to the primary coil")`
or `eta=("Output power")/("Input power")`
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%`
Note The efficiency of an ideal transformer is 1 (or 100%). But in practice due to loss in energy, the efficiency of trensformer is always less than 1 (or less than 100%)