Question

A wire of mass $m$, length $l$, density $d$ and area of cross section A is stretched in such a way that its length increases by 10% of its original value. Express the changed resistance in percentage.

Answer 1

Resistance is given as ; $R=\frac{\rho l}{A}$

$R^{\prime }=\frac{\rho l^{\prime }}{A}$

$l^{\prime }=l+\frac{10}{100}l=1.1l$

Percentage change in resistance = $\frac{R^{\prime }-R}{R}\times 100$=$\frac{\rho }{A}\left(100\right)(1.1l-l)/l$=10%