Question

A transformer is used to light 140W,24 V lamp form a 240 V ac mains. If the main current is 0.7 A, the

efficiency of the transformer is

• A. 63.8%
• B. 74%
• C. 83.3%
• D. 48%

Answer 1

Answer: (C)

83.3%

Answer 2

: Output power = 140 W

Input power = $240 \times 0.7 = 168W$

Efficiency= $\frac{Outputpower}{inputpower} \times 100 = \frac{140}{168} \times 100 = 83.3\%$