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JAMB Physics 2001 Question 36

Question 36

Current Electricity

A cell can supply currents of 0.4 A and 0.2 A through a 4.0 Ω and 10.0 Ω resistors respectively. The internal resistance of the cell is

  1. A.2.0 Ω
  2. B.1.0 Ω
  3. C.2.5 Ω
  4. D.1.5 Ω
Show the answer and explanation

Answer: A (2.0 Ω)

Explanation

E = 0.4(4 + r) = 0.2(10 + r), so 1.6 + 0.4r = 2 + 0.2r, giving 0.2r = 0.4 and r = 2.0 Ω.