Question

The balancing length for a cell is $560cm$ in a potentiometer experiment. When an external resistance of $10\Omega$ is connected in parallel to the cell, the balancing length changes by $41cm$. The internal resistance of the cell in ohms is

• A. $1.6$
• B. $1.4$
• C. $12$
• D. $0.8$

Answer 1

The correct option is D $0.8$

Given,

$R=10\Omega$

$l_1=560cm,l_2=560-41=519cm$

To find,

Internal resistance of cell, $r=?$

$r=R(\frac{l_1}{l_2}-1)=10(\frac{560}{519}-1)=10\left(\frac{560-519}{519}\right)=10\left(\frac{41}{519}\right)=10\times 0.078=0.78$

$\Rightarrow r=0.78\Omega \simeq 0.8\Omega$

Therefore, the internal resistance of the cell is $0.8\Omega$