Question

A wire of resistance 5 ohm is stretched to such a length that its becomes half what will be its new resistance

Answer 1

Answer:1/4 times of older resistance

Explanation: earlier resistance was: R=pL/A

New length L'=1/2L

Area will also be changed but volume remains same so...

A'L'=AL. (volume =area ×length )

A'=AL/L'

A'=2AL/L

So new area is twice of old one

Now new resistance is:

R'=pL'/A'. p=resistivity of wire

R'=pL/2×2A

R'=1/4 pL/A

R'=1/4R