First slide

potentiometer

Question

The resistance of a potentiometer wire of length 200cm is $10 Ω$ . This wire is connected in series with a 20 v battery and an external resistance of $30 Ω$ . What will be the balancing length of a secondary cell of emf 4 volt?

Moderate

A

120cm
B

160cm
C

180cm
D

140cm

Solution

Current in the potentiometer wire is given by $i = \frac{20}{10 + 30} A = 0.5 A$
Potential gradient $= \frac{0.5 x 10}{200} v / cm = \frac{1}{40} v / cm$
If x cm be the balancing length, Then
$\frac{1}{40} \times x = 4 \Rightarrow x = 160 cm$

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