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. 0.025
B. 0.005
C. 0.01
D. 0.02

Explanation

`R=(pl)/A prop l/A`
If volume is constant Al= constant `implies R prop l^2 prop 1/A^2`
Now, `R_2/R_1=(l_2/l_1)^2 , l_2=l_1+0.5/100 l_1 implies R_2/R_1=(1+0.5/100)^2 (1+(2times 0.5)/100)=101/100`
`implies (R_2-R_1)/R_1=1/100 1%` i.e., Option ( C)