Question

In a potentiometer experiment, it is found that no current passes through the galvanometer when the terminals of the cell are connected across $52cm$ of the potentiometer wire. If the cell is shunted by the resistance of $5\Omega$, a balance is found when the cell is connected across $40cm$ of the wire. Find the internal resistance of the cell.

• A. $2\Omega$
• B. $2.5\Omega$
• C. $1\Omega$
• D. $1.5\Omega$

Answer 1

The correct option is D $1.5\Omega$

Step 1, Given data

Balancing length in first case $l_1$ = 52 cm

Balancing length in second case $l_2$ = 40 cm

Shunt resistance = 5 ohm

Step 2, Finding the internal resistance

We know,

For the internal resistance

Using Formula

$r=R(\frac{{\ell }_1}{{\ell }_2}-1)$

On putting given values, we get

$r=5(\frac{52}{40}-1)=5\times \frac{12}{40}=1.5\Omega$

Hence the internal resistance is 1.5 ohm