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JAMB Physics 1983 Question 39

Question 39

Current Electricity

The difference of potential between the terminals of a cell is 2.2 volts. When a 4 ohm resistor is connected across the terminals of this cell, the potential difference is 2 volts. What is the internal resistance of the cell?

  1. A.0.10 ohms
  2. B.0.25 ohms
  3. C.0.40 ohms
  4. D.2.50 ohms
  5. E.4.00 ohms
Show the answer and explanation

Answer: C (0.40 ohms)

Explanation

Current I = 2/4 = 0.5 A. Lost volts = 2.2 − 2 = 0.2 V, so r = 0.2/0.5 = 0.4 Ω.