A wire of length 10 cm and radius 7 × 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 × 10 - 7 Ω m , then value of R is :

Question

A wire of length 10 cm and radius 7 × 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 × 10 - 7 Ω m , then value of R is :, 63, 70, 66, 35

MARKS App · Accepted Answer

From the null point condition of a Meter Bridge, it follows that, 4 . 5 Ω 60 = X 100 - 60 ⇒ X = 40 60 × 4 . 5 Ω = 3 Ω Also, X = ρ l A = ρ l π r 2 . . . 1 From equation (1), it follows that 3 = ρ × 0 . 1 π × 7 × 10 - 4 2 ⇒ ρ = 3 × π × 7 × 10 - 4 2 0 . 1 ≈ 66 × 10 - 7 Ω m Therefore, R = 66 .

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