Question

The resistance of a wire is $5 \Omega$. It's new resistance in ohm if stretched to 5 times of it's original length will be:

• A. $125$
• B. 5
• C. 25
• D. 625

Answer 1

Answer: (A)

$125$

Answer 2

The correct answer is (A) : 125

∵ Volume of wire is constant in stretching
Vi​=Vf​
Ai​ℓi​=Af​ℓf​
Aℓ=A′(5ℓ)
A′=5A​
Rf​=Af​ρℓf​​=(5A​)ρ(5ℓ)​
=25(Aρℓ​)
=25×5=125Ω