If a wire is stretched to make it 0.1 % longer the percentage change in its resistance would be:

Options

A. Zero
B. 0.002
C. 0.001
D. 0.004

Answer

C

Explanation

Volume V = lA
`(Delta A)/A = -(Delta l)A`
Since volume does not change
`(Delta A)/A = - (Delta l)/A" …(1)"`
`R = (rho l)/A`
` :." "(Delta R)/R = (Delta l)/l - (Delta A)/A`
From (1) `(Delta R)/R = (Delta l)/l - ( -(Delta l)/l) `
` = (2Delta l)/l = 2 xx 0.1 = 0.2 %`