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 %

Explanation

Here, `I_(P) = ?, E_(P) = 200 V, E_(s) = 20 V, R_(s) = 20 ohm`,
`I_(s) = (E_(s))/(R_(s)) = (20)/(20) = 1A`
As `eta = (E_(s) I_(s))/(E_(P) I_(P))`
`:. (80)/(100) = (20 xx 1)/(200 I_(P)) , I_(P) = (1)/(8) = 0.125 A`