A null point is found at 200 ,cm in potentiometer when cell in se… - Vidyadip

MCQ

A null point is found at $200\,cm$ in potentiometer when cell in secondary circuit is shunted by $5\,\Omega$. When a resistance of $15\,\Omega$ is used for shunting null point moves to $300\,cm$. The internal resistance of the cell is $..............\,\Omega$.

A
$4$
✓
$5$
C
$3$
D
$2$

✓

Answer

Correct option: B.

$5$

b
$\frac{\varepsilon}{ r +5} \times 5=200\,x$

$\frac{\varepsilon \times 15}{ r +15}=300\,x$

$\Rightarrow r =5$

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