A wire of length 10 cm and radius m connected across the right gap of a meter bridge. When a resistance of is connected on the left gap by using a resistance box, the balance length is found to be at 60 cm from the left end. If the resistivity of the wi

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Solution

Q.
A wire of length 10 cm and radius $\sqrt{7} \times 10^{- 4}$ m connected across the right gap of a meter bridge. When a resistance of $4.5 Ω$ is connected on the left gap by using a resistance box, the balance length is found to be at 60 cm from the left end. If the resistivity of the wire is $R \times 10^{- 7} Ω m,$ then value of R is [2024]

1 63

2 70

3 66

4 35

Ans.
(3)

$For null point, \frac{4.5}{60} = \frac{R^{'}}{40}$

Also, $R^{'} = \frac{ρ l}{A} = \frac{ρ l}{π r^{2}}$

$4.5 \times 40 = ρ \times \frac{0.1}{π \times 7 \times 10^{- 8}} \times 60$

$ρ = 66 \times 10^{- 7} Ω \times m$

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