Question

In an experiment to measure the internal resistance of a cell by potentiometer, it is found that the balance point is at a length of 2 m when the cell is shunted by a $5\Omega$ resistance; and is at a length of 3 m when the cell is shunted by a $10\Omega$ resistance. The internal resistance of the cell is, then

• A. $1.5\Omega$
• B. $10\Omega$
• C. $15\Omega$
• D. $1\Omega$

Answer 1

The correct option is B $10\Omega$

By using $r=\left(\frac{l_1-l_2}{l_2}\right)R^{{}^{\prime }}\Rightarrow r=\left(\frac{l_1-2}{2}\right)\times 5$ ........(i)
and $r=\left(\frac{l_1-3}{3}\right)\times 10$ ........(ii)
On solving (i) and (ii) r $=10\Omega$