In a potentiometer experiment, a cell in the secondary circuit gives null point at 2.5 m when the length of the potentiometer wire is 10 m. If the length of the potentiometer wire is increased by 1 m

Question

In a potentiometer experiment, a cell in the secondary circuit gives null point at 2.5 m when the length of the potentiometer wire is 10 m. If the length of the potentiometer wire is increased by 1 m without changing the cell in the primary circuit, then the position of the null point will be

TestHub · Accepted Answer

The resistance of a potentiometer wire is given as,

$R = ρ \times \frac{l}{A}$

$R^{'} = \frac{2 .5 ρ}{A \times 10}$

Potential $V' = I \times R'$ ,

$= I \{\frac{2.5 ρ}{A \times 10}\}$

Now, again the length of potentiometer wire is increased by $1 m$ , then the resistance of null position wire.

$R^{''} = \frac{ρ \times l}{11 \times A}$

$V " = IR "$

and, $V' = V "$

$\frac{I \times 2 .5 ρ}{A \times 10} = \frac{I \times ρ \times l}{11 \times A}$

$\frac{2 .5 \times 11}{10} = l = 2.75 m$

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