Question

A copper wire iis stretched to make it `0.1%` longer. What is the percentage change in its resistance?

Answer 1

`R=rho 1/A=(rhol)/(V/l)` (`V=` volume of wire)
`=(rhol^2)/V`
`:. R propl^2` (`rho "and" V=` constant)
For small percentage change
% change `R=2(%"change in" l)=2(0.1%)=0.2%`
Since `Rpropl^2`, with increase in the value of `l`, resistance will also increase.