Question

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

• A. $10\%$
• B. $50\%$
• C. $60\%$
• D. $90\%$

Answer 1

The correct option is D $90\%$

Given,

The mains current is $0.5A$.

The mains voltage is $220V$.

Power of light $=100W$and voltage $V=110V$

The efficiency is $n=\frac{\text{output}}{\text{input}}\times 100=\frac{100}{220\times 0.5}\times 100=90.9$

The approximate efficiency of transformer is $90\%$.

Therefore the correct option is $D$.