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. `91%`
B. `100%`
C. `95%`
D. `55%`

Answer

A

Explanation

Here, `P_(0) = 100 W, E_(P) = 220 V, I_(P) = 0.5 A`
`eta (P_(0))/(P_(i)) = (P_(0))/(E_(P) I_(P)) = (100)/(220 xx 0.5) = (10)/(11) = (10)/(11) xx 100%`
`= 91%`