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_sI_s)/(V_p I_p ) `
Given , ` V_sI_s = 100 W`,
` V_p = 220 V, I _ p = 0.5A `
Hence, ` eta = (100)/(220 xx 0.5 ) = 0.90 = 90 % `