Question

A transformer is used to light $100 \,W - 110\, V$ lamp from $220\, V$ mains. If the main current is $0.5\, A$, the efficiency of the transformer is

• A. 0.9
• B. 0.95
• C. 0.96
• D. 0.99

Answer 1

Answer: (A)

0.9

Answer 2

Given, output power $= 100\, W$
$V =220 \,V, I = 0.5 \,A$
We know that,
Efficiency $=\frac{\text{output power}}{\text{input power}}\times100$
$=\frac{100}{220\times0.5}\times100$
$=90\%$