A copper wire is stretched to make it `0.5%` longer. The percentage change in its electrical resistance if its volume remains unchanged is :

Options

A. `2.5% `
B. `0.5%`
C. `2.0%`
D. `1.0%`

Answer

D

Explanation

`(Deltal)/l = 0.5% implies (DeltaA)/A =-0.5%`
`R =rho(l)/A`
`(DeltaR)/R=(Deltal)/l-(DeltaA)/(A)=(DeltaR)/R=0.5%+0.5%=1%`