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Question
What should be the length of a nickel wire of area of cross-section 3 mm2 used for making a rheostat of 750 ohm? (ρ of nickle = 0.069 Ohm mm2/m)
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Solution
Specific resistance = ρ = 0.069 ohm `"mm"^2/"m"`
R = 750 W
A = 3mm2
as I = `("R" xx "A")/ρ = (750 xx 3)/0.069`
∴ length l = 32608.7 metre
The length of a nickel wire should be 32608.7 m.
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