Question

We stretch a wire of resistance $R$ such that its length increases by 20%. Then the percentage change in its resistance will be?

• A. 20%
• B. 44%
• C. 10%
• D. 40%

Answer 1

The correct option is B 44%

New length = 1.2L
When we stretch a wire to increase it's length without changing it's volume then:
$\frac{R_1}{R_2}=(\frac{l_1}{l_2}{)}^2\Rightarrow \frac{R_1}{R_2}=(\frac{L}{1.2L}{)}^2=\frac{1}{1.44}$
$R_2=1.44R_1\Omega$
$\therefore$Percentage change in R=$\frac{R_2-R_1}{R_1}\times 100$$\Rightarrow 44\%$