An incandescent bulb produces 520 lumens and has an efficacy of 13 lm/W.
Answer
A
2.5 W
B
40 W
C
503 W
D
533 W
Explanation
Efficacy is luminous output per unit of electrical power, so power = lumens ÷ efficacy. For this bulb, 520 lm ÷ 13 lm/W = 40 W; therefore, the correct choice is 40 W.
AI-written and checked against the verified answer.