A transformer is an electrical device which is used for changing the a.c. voltage. It is based on the phenomenon of mutual induction. It can be shown that
`(E_(s))/(E_(P)) = (I_(P))/(I_(s)) = (n_(s))/(n_(P)) = K`
Where the symbols have their standard meaning. For a step up transformer, `K gt 1` and for a step down transformer, `K lt 1`. The above relations are on the assumption that efficiency to transformer is `100%` . In fact, efficiency
`eta = ("output power")/("input power") = (E_(s) I_(s))/(E_(P) I_(P))`
The number of turns in the primary and secondary coils of a transformer are `2000` and `50` respectively. The primary coil is connected to main supply of `120 V` and secondary to a night bulb `0.6 Omega`. The efficiency of transformer is `80%`.
Power in secondary coil is:

Options

A. `15 W`
B. `225 W`
C. `120 W`
D. `7 W`

Answer

A

Explanation

Power in secondary coil is ` = E_(s) I_(s)`
`= 3 xx 5 = 15 W`