Calculate current drawn by primary coil of a transformer, Which steps down 200 V to 20 V to operate a device of 20 ohm resistance. Assume efficiency of transformer 80 %.

Explanation

Here `V_(P)=200 V,V_(S)=20, R_(S)=20 Omega`, efficiency `(eta)=80%`
`I_(S)=V_(S)/R_(S)=20/10=1A`
Efficiency `eta=(V_(S)I_(S))/(V_(P)I_(P))` or `80/100=(200xx1)/(200xxI_(p))`
`[because ="Power output"/"Power input"]`
or `I_(P)=0.125 A`