Question

A transformer ia used to light a 100W and 110V lamp from a 220V mains. If the main current is 0.5amp ,the efficiency of the transformer is approx

1)10%

2)30%

3)50%

4)90%

Answer 1

Power of the main = Vmain× Imain
= 220 ×0.5
= 110 Watt

Pin = 110 Watt

Pout =100 Watt

efficiency = Pout/Pin = (100/110)×100 =90.9%