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. 0.25
D. 0.4 A

Answer

B

Explanation

`P = VI`
For secondary
`V_(2)=(P_(2))/(I_(2))=(500)/(12.5)=40` volts
For an ideal transformer (100 % efficient)
`P_("input")=P_("output")`
`rArr V_(1)I_(1)=V_(2)I_(2)`
`rArr I_(1) =(V_(2)I_(2))/(V_(1))=(40(12.5))/(40xx5)=2.5A`
`[because (n_(1))/(n_(2))=(V_(1))/(V_(2))rArr (5)/(1)=(V_(1))/(40)]`