First slide

meter bridge

Question

In a metre bridge experiment, null point is obtained at 20 cm from one end of the wire when resistance X is balanced against another resistance Y. If X < Y, then where will be the new position of the null point from the same end, if one decides to balance a resistance of 4X against Y?

Moderate

A

50 cm
B

80 cm
C

40 cm
D

70 cm

Solution

In balancing condition, $\frac{R_{1}}{R_{2}} = \frac{l_{1}}{l_{2}} = \frac{l_{1}}{100 - l_{1}}$
$\Rightarrow \frac{X}{Y} = \frac{20}{80} = \frac{1}{4}$ ….(i)
$and \frac{4 X}{Y} = \frac{l}{100 - l}$ ….(ii)
$\Rightarrow \frac{4}{4} = \frac{l}{100 - l} \Rightarrow l = 50 cm$

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