Question

how is the resistance of a wire affected if its radius is doubled

Answer 1

Hii There!!

Since, R= rhow×l / A
or , R = rhow × l/ πr2

=) Here, Resistance of a wire is inverself proportional to the area of cross-section.

So, when we double the radius, it will increase the cross-section of the wire four-times.



Hope it helps
#DK

Answer 2

Resistance is given by:
R=ρ×l / A

ρ: Resistivity
l:  length
A: Area

R∝$\frac{1}{Area}$           (A=πr²)
R∝$\frac{1}{ r^{2} }$

When radius is doubled, Resistance decreased 2² times which is 4.

Hence when radius is doubled resistance decreases 4 times