First slide

potentiometer

Question

The e.m.f. of the driver cell of a potentiometer is 2V and its internal resistance is negligible. The length of the potentiometer wire is 100 cm and resistance is 5 ohms. How much resistance is to be connected in series with the potentiometer wire to have a potential gradient of 0.05 $m V c m^{- 1}$ ?

Moderate

A

1990 ohms
B

2000 ohms
C

1995 ohms
D

1920 ohms

Solution

$p o t e n t i a l g r a d i e n t = \frac{i R_{P}}{L} = \frac{E R_{P}}{L (R_{s} + R_{P})} = \frac{0.05 x 10^{- 3}}{10^{- 2}} V / m \frac{2 x 5}{1 (R_{s} + 5)} = 5 x 10^{- 3} R_{s} = 1995$

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