The increased resistance of a wire if its length is doubled and original cross sectional area is halved will be: (Given R = original resistance of wire)

4R

The correct answer is Option (3) → 4R

Resistance of a wire is,

$R=ρ\frac{l}{A}$

$l$ = length of wire

A = Cross-section area

when $l'=2l$ and $A'=A/2$

$R'=ρ\frac{2l}{A/2}=4ρ\frac{l}{A}$=4R$