Question

In a potentiometer experiment of a cell of emf $1.25V$ gives balancing length of $30cm$. If the cell is replaced by another cell, balancing length is found to be $40cm$. What is the emf of second cell ?

• A. $\simeq$ 1.57 V
• B. $\simeq$ 1.67 V
• C. $\simeq$ 1.47 V
• D. $\simeq$ 1.37 V

Answer 1

Answer: (B)

Given,
First balancing length
$l_1=30cm$
Second balancing length
$l_2=40cm$
$E_1=1.25V$
$E_2$ =?
So, according to the principle of potentiometer
$E_1=K{l}_1\dots (i)$
$E_2=K{l}_2\dots (ii)$
$\frac{E_1}{E_2}=\frac{K{l}_1}{K{l}_2}$
$\frac{1.25}{E_2}=\frac{30}{40}$
$\Rightarrow E_2=\frac{1.25\times 40}{30}$
$\Rightarrow E_2=\frac{5}{3}$
$E_2=1.666V$
$\simeq 1.67V$