Question

In a potentiometer the balancing with a cell is at length of $220$cm. On shunting the cell with a resistance of $3\Omega$ balance length becomes $130$cm. What is the internal resistance of this cell?

• A. $4.5\Omega$
• B. $7.8\Omega$
• C. $6.3\Omega$
• D. $2.08\Omega$

Answer 1

The correct option is D $2.08\Omega$

Given that,

Initial balancing length of potentiometer with a cell, $l_1=220cm$

Now the cell is shunted with resistance, $R=3\Omega$

Final balancing length, $l_2=130cm$

Internal resistance of the cell, $r=(\frac{l_1-l_2}{l_2})R$

$⟹r=(\frac{90}{130})\times 3=\frac{270}{130}=2.08\Omega$

Hence, option $\left(D\right)$ is correct.