A meter bridge is used to determine the resistance of an unknown wire by measuring the balance point length l . If the wire is replaced by another wire of same material but with double the length and half the thickness, the balancing point is expected to be

Question

A meter bridge is used to determine the resistance of an unknown wire by measuring the balance point length l . If the wire is replaced by another wire of same material but with double the length and half the thickness, the balancing point is expected to be, 1 8 l, 1 4 l, 8 l, 16 l

MARKS App · Accepted Answer

In a meter bridge the ratio of two resistances is R R ′ = l l ′ Where l and l ′ are balancing lengths. Resistance R = ρ l A = ρ l π r 2 In material remains same ρ = ρ ′ Given, l ′ = 2 l r ′ = r 2 ∴ R ′ = ρ l ′ A ′ = ρ 2 l π r 2 2 = 8 ρ l π r 2 R ′ = 8 R Therefore, the new balancing point is expected to be 8 l .

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