First slide

Electrical measuring instruments

Question

The length of potentiometer wire is 1200cm and it carries a current 30 mA. For a cell of emf 5V and internal resistance of $20 Ω$ . The null point on it is found to be at 1000 cm. The resistance of whole wire is

Easy

A

$200 Ω$
B

$100 Ω$
C

$300 Ω$
D

$120 Ω$

Solution

Potential gradient $= \frac{5}{1000} = \frac{V_{p}}{1200}$
$V_{p} = 6V$
$R_{p} = \frac{V_{p}}{I} = \frac{6}{30 \times 10^{- 3}} = 200 Ω$

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