Question

A wire of length L and resistance R is stretched so that the length is doubled and area of cross section halved. How will (i) resistance change and (ii) resistivity change.

Answer 1

$\Rightarrow$ Length $\left(l\right)$ is doubled & Area of cross section (A) is halved.

$l$ becomes $2l$ & A becomes $\frac{A}{2}$

$R=P\frac{L}{A}$

now take $l=2l,A=\frac{A}{2}$

$R=\frac{P2l}{A/2}=4P\frac{L}{A}\Rightarrow 4R$

Resistance becomes 4 times

1) Resistivity does not depend on its length 02 Area.

Hence, it does not change.