The resistance of a 40W car headlamp; drawing current from a 12V battery is?

A. 0.3Ω
B. 3.3Ω
C. 3.6Ω
D. 4.8Ω

Correct Answer:

Option C – 3.6Ω

Explanation

Power delivered to headlamp = V²/R
= 40W

R = V²/40
= (12²)/40
= 3.6Ω