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JAMB Physics 2013 Paper

Question : 31

Total: 43

Solution:

Concept:

The cell’s emf is used to drive current through both the external resistor and the cell’s internal resistance.

Explanation:

Using the circuit equation:

E = I(R + r)

Make

r

the subject of the formula:

r = \frac{E}{I} - R

Substitute the given values:

E = 1.5\,\mathrm{V}

I = 0.3\,\mathrm{A}

R = 1\,\Omega

r = \frac{1.5}{0.3} - 1 = 5 - 1 = 4\,\Omega

Answer:

Internal resistance

r = 4.0\,\Omega

. Correct option: A.

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