A step down transformer of efficiency `80%` is used on a 1000V line to deliver a current of 20 A at 120 V at the secondary coil. What is the current drawn from the line?

Options

A. 0.3 A
B. 30 A
C. 2.4 A
D. `2 A`

Answer

D

Explanation

`V_(p) = 1000 V , V_(s) = 120 V and I_(s) = 20 A`
For an ideal transfomer, `V_(p) xx I_(p) = V_(s) xx I_(s)`
`:. I_(p) = (120 xx 20)/(1000) = 2.4 A`
But for the given transformer, the efficiency is `80%`
`:. I_(p)` should be `2.4 xx 100/80 = 3A`.