A 120V; 60W lamp is to be operated on 220V A.C the supply mains. Calculate the values of non-inductive resistance that would be required to ensure that the lamp is run on current value.

A. 100 Ω
B. 200 Ω
C. 300 Ω
D. 500 Ω

Correct Answer:

Option B – 200 Ω

Explanation

Power of the lamp = 60W = (V²)/R and the voltage rate = 120v.
R = (V²)/60 = (120 X 120)/60 = 240 Ω, the fuse wire that should ensure current does not exceed this value should be rated 200 Ω