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JAMB Physics 1979 Question 29

Question 29

Electrical Energy and Power

The bulb of a motorcycle head-lamp is marked 40 W, 6 V. The resistance of the filament when it is switched on is

  1. A.62/402 ohms
  2. B.40/62 ohms
  3. C.40/6 ohms
  4. D.6 × 40 ohms
  5. E.62/40 ohms.
Show the answer and explanation

Answer: E (62/40 ohms.)

Explanation

P = V²/R, so R = V²/P = 6²/40 Ω (0.9 Ω).