Question

The Daniel cell is balanced on $125\, cm$ length of a potentiometer. Now, the cell is short circuited by a resistance of $2\, \Omega$ and the balance is obtained at $100\, cm$. The internal resistance of the denial cell is

• A. $\frac{4}{3}\, \Omega$
• B. $1.5\, \Omega$
• C. $1.25\, \Omega$
• D. $0.5\, \Omega$

Answer 1

Answer: (D)

$0.5\, \Omega$

Answer 2

Here , $r = R \left(\frac{I_{1}}{I_{2}} - 1\right)$
$= 2 \left(\frac{125}{100} - 1\right)$
$= 2\left(\frac{5}{4} - 1 \right)$
$= 2 \times\frac{1}{4}$
$= 0.05\, \Omega$