The secondary coil of an ideal step down transformer is delivering 500 watt power at `12.5 A` current. If the ratio of turns in the primary to the secondary is `5 : 1` then the current flowing in the primary coil will be:

Options

A. `62.5 A`
B. `2.5 A`
C. `6 A`
D. `0.4 A`

Answer

B

Explanation

For an ideal transformer (100% efficient)
`rArr P_("in put") = P_("output") V_(1) I_(1) = V_(2) I_(2)`
`rArr I_(1) = (V_(2) I_(2))/(V_(1)) = (40 (12.5))/(40 xx 5) = 2.5 A`
`[:' (n_(1))/(n_(2)) = (V_(1))/(V_(2)) implies (5)/(1) = (V_(1))/(40)]`