A transformer powers a 100 W, 110 V lamp from a 220 V mains supply. If the mains current is 0.5 A, determine its efficiency.
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A transformer powers a 100 W, 110 V lamp from a 220 V mains supply. If the mains current is 0.5 A, determine its efficiency.

G1 Physics · Accepted Answer

Step 1: Useful output power is the lamp rating P(out)=100W. Step 2: Primary input power is P(in)=VₚIₚ=220×0.5=110W. Step 3: Efficiency η=P(out)/P(in)=100/110≈0.9091=90.9%. Answer B (90%). Final answer: (B) 90%.