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JAMB Physics 1985 Question 38

Question 38

Current Electricity

A cell gives a current of 0.15 A through a resistance of 8 Ω and 0.3 A when the resistance is changed to 3 Ω. The internal resistance of the cell is

  1. A.0.05 Ω
  2. B.1.00 Ω
  3. C.1.50 Ω
  4. D.2.00 Ω
  5. E.2.50 Ω
Show the answer and explanation

Answer: D (2.00 Ω)

Explanation

E = 0.15(8 + r) = 0.3(3 + r). So 1.2 + 0.15r = 0.9 + 0.3r, giving 0.15r = 0.3 and r = 2 Ω.