Question

Study the circuit diagram in the figure, and hence, calculate the internal resistance of the cell.

Answer 1

\[E = 1.5\text{ V};\ V = 1.2\text{ V};\ R_1 = 3\text{ Ω};\ R_2 = 6\text{ Ω};\ r = ?\]

The external resistance is

\[R = \frac{R_1 R_2}{R_1 + R_2}\]

\[= \frac{3 \times 6}{3 + 6}\]

\[= 2\text{ Ω}\]

\[r = \frac{R(E - V)}{V}\]

\[= \frac{2(1.5 - 1.2)}{1.2}\]

\[= \frac{2 \times 0.3}{1.2}\]

\[= 0.5\text{ Ω}\]