Question

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

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

Answer 1

Answer: (B)

$1.5 \Omega$

Answer 2

$\because E \propto I_{1}$
and $E-i r \propto I_{2}$
$\therefore \frac{E}{E-i r}=\frac{I_{1}}{l_{2}}$
$\Rightarrow \frac{E}{E-\left(\frac{E}{r+5}\right) \times r}=\frac{52}{40}$
$\Rightarrow \frac{r+5}{5}=\frac{13}{10}$
$\Rightarrow r=1.5\, \Omega$