Calculate the current drawn by the primary of a tarnsformer which steps down 200 V to 20 V to operate a device of resistance 20 ohm. Assume the efficiency of transformer to be 80 %

Options

A. `0.125 A`
B. `0.225 A`
C. `0.325 A`
D. `0.425 A`

Answer

A

Explanation

Given:
`V _(p) = 20 0 V , R = 2 0 Omega, V _(s) = 20 V , eta = 80%`
Current through the secondary coil is
`I _(s) = ( V _(s))/(R) = ( 20 V)/( 20 Omega ) = 1 A`
Efficienct of transformer
`eta = ("Output power")/("Input power") = (V _(s) I _(s))/( V _(p) I _(p))`
or `I _(p) = (V _(S)I _(S))/( V _(p) eta)= (20 xx 1 xx 100)/( 200 xx 80) = 0. 125 A`