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JAMB Physics 1978 Question 25

Question 25

Electrical Energy and Power

Two lamps rated 40 W and 220 V each are connected in series. The total power dissipated in both lamps is

  1. A.10 W
  2. B.20 W
  3. C.40 W
  4. D.80 W
  5. E.none of the above.
Show the answer and explanation

Answer: B (20 W)

Explanation

Each lamp has resistance R = V²/P = 220²/40 = 1210 Ω, so in series on a 220 V supply the total resistance is 2420 Ω and the power is 220²/2420 = 20 W.