Question

If length remain same and diameter double then new resistance

Answer 1

The formula of resistance, R =  r (resistivity constant) x L/A

According to question,

Please note either diameter or radius are doubled, they meant the same,

here i am taking radius (r) for convenience,

So as Resistance inversely proportional to Radius Square, when Radius is 2 times then Resistance is 1/2² or 1/4.

we have R = r x L/A

and, R1 = r x L/4A = 1/4 ( r x L/A)

= 1/4 xR = R/4