Question

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

$\simeq$ 1.67 V

Answer 2

Given, First balancing length $l_{1}=30\, cm$ Second balancing length $l_{2} =40\, cm$ $E_{1} =1.25\, V$ $E_{2}$ =? So, according to the principle of potentiometer $E_{1} =Kl_{1}\,\,\,\,\,\dots(i)$ $E_{2} =K l_{2}\,\,\,\,\dots(ii)$ $\frac{E_{1}}{E_{2}} =\frac{Kl_1}{Kl_2}$ $\frac{1.25}{E_{2}} =\frac{30}{40}$ $\Rightarrow E_{2} =\frac{1.25 \times 40}{30}$ $\Rightarrow E_{2}=\frac{5}{3}$ $E_{2} =1.666\, V$ $\simeq 1.67\, V$