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A copper wire is stretched to make it 0.2% longer. What is the percentage change in its resistance?

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The mass m of the wire of length l, area of cross section A and density d is givne by
`m=Ald or A=(m)/(ld)`
The resistance R of the wire of resistivity `rho` is given by
`R= (rho l)/(A) = (rho l^(2)d)/(m)= k l^(2)`
Where `k=(rho d)//(m)` is a constant of the wire.
`:. (dR)/(R) xx 100 = (2 xx 0.2)/(100) xx 100=0.4%`.

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