Question

When the area of cross-section of a conductor is doubled, its resistance becomes:

(a) double
(b) half
(c) four time
(d) one-fourth

Answer 1

(b) half
We know that the resistance of a conductor is given by:
$\mathrm{R}=\mathrm{\rho }\frac{\mathrm{l}}{\mathrm{A}}$
where ρ = resistivity
l = length of the conductor
A = area of the cross-section of the conductor
Let the new resistance be R' when the area of cross-section of the conductor is doubled
${\mathrm{R}}^{,}=\mathrm{\rho }\frac{\mathrm{l}}{2\mathrm{A}}$

Thus, the new resistance becomes half of the previous one.