JAMB - Physics (1988 - No. 30)

When a resistance R is across a cell, the voltage across the terminals of the cell is reduced to two-third of its normal value. The internal resistance of the cell is
\(\frac{2}{1}\)R
\(\frac{1}{2}\)R
\(\frac{3}{2}\)R
5R

Explanation

IR = \(\frac{2}{3}\) I(R + r)

r = \(\frac{1}{2}\)R

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