Question

In a potentiometer experiment, two cells of emf $E_1$ and $E_2$ are used in series in the secondary circuit. The balancing length is found to be 58 cm. If the polarity of $E_2$ is reversed, the balancing length becomes 29 cm. The ratio $E_1/E_2$ of the emfs of two cells is :

• A. 1:01
• B. 2:01
• C. 3:01
• D. 4:01

Answer 1

The Correct Option is B

Using, V $\propto \, l$ we get $\frac{E_1 + E_2}{E_1 - E_2} = \frac{l_1 + l_2}{l_1 - l_2} = \frac{58 + 29}{58 - 29} = \frac{3}{1}$
$i.e.$ $\frac{E_1}{E_2} = \frac{2}{1}$ $\left( \, \because \, \frac{E_1 + E_2 + E_1 - E_2 }{E_1 + E_2-(E_1-E_2)} = \frac{3 + 1}{3 - 1} \right)$