Question

We have a copper wire of Resistance R. This wire is polled so that its length is doubled (temperature
remains constant). Find the few resistance of the wire in terms of its original resistance. 121
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Answer 1

let original resistance of the wire be = R

let few resistance of wire be = r

We know that ,

R is directly proportional to l(length) by a

( area of cross section)

R = specific resistance(q) × l/a. -(1)

So A.T.Q,

r = q × 2× l/a

r = 2 × ( q × l/a)

By (1)

r = 2 × R

r = 2 × 121

r = 242 ohm

Hope its correct.