Question

Find new resistance of wire if it is stretched to twice its original length . Original resistance was 20 ohm . Also how its resistivity will change.

Answer 1

Dear student

R = 20 Ohm
R' = ?
Let length = l
New length = 2l

Volume remains same.
area of cross section = a
new area of cross section = a'

R = pl/a = 20
R' = p 2l / (a/2)

R' = 4 pl/a
Put value of R = pl/a

R' = 4 × 20 = 80 Ohm

Regards