Question

A potentiometer wire of length $10m$ and resistance $20\Omega$ is connected in series with a $15V$ battery and an external resistance $40\Omega$ . A secondary cell of emf in the secondary circuit is balanced by $240cm$ long potentiometer wire. The emf $E$ of the cell is

• A. 2.4 V
• B. 1.2 V
• C. 2.0 V
• D. 3 V
• E. 6 V

Answer 1

Answer: (B)

Total resistance or $R=20+40$
$R=60\Omega .$
Given: $V=15$ volt current $I=\frac{V}{R}=\frac{15}{60}$
$I=0.25A$
Potential gradient $=\frac{V}{l}$
$\frac{20\times 0.25}{10}$
$=0.5V{m}^{-1}$
Potential difference across 240 cm
$E=0.5\times 2.4$ $E=1.2V$