Q. A transformer is used to light a 100 W and 110 V lamp from a 220 V mains. If the main current is 0.5 amp, the efficiency of the transformer is approximately
A) 50%
B) 90%
C) 10%
D) 30%
Explanation
[Solution from source] Efficiency = output/input = 100/(220 × 0.5) = 100/110 ≈ 0.91, i.e. about 90%. 50% comes from comparing the voltages instead of the powers. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.