Q29 of 31 Page 252

A uniform wire of resistance 100 Ω melted and recast into wire of length doubles that of the original. What would be the resistance of the new wire formed?

Given R of original wire = 100 ohm


When length is l, R = 100 ohm


When length is 2l, R’ = ?


We know R = ρ l/A


R’ = ρ 2l/A


R’ = 2 ρ l/A


R’ = 2R [ since ρ l/A = R]


So R’ = 2 x 100


R’ = 200 ohm


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