Question

A wire of a certain material is stretched slowly by ten percent. Its new resistance and specific resistance become respectively

• A. both remain the same
• B. 1.1 times, 1.1 times
• C. 1.2 times, 1.1 times
• D. 1.21 times, same

Answer 1

Answer: (D)

1.21 times, same

Answer 2

$\frac{\Delta l}{l}=0.1 \therefore l = 1.1$
but the area also decreases by 0.1.
mass $=\rho lA =V\rho.$ $ln\,l+ln\, A = ln\,$ mass.
$\therefore\, \, \frac{\Delta l}{l}+\frac{\Delta A}{A}=0 \, \, \Rightarrow \, \frac{\Delta l}{l}+\frac{-\Delta A}{A}$
Length increases by 0.1, resistance increases, area decreases by 0.1, then also resistance will increase.
Total increase in resistance is approximately 1.2 times, due to increase in length and decrease in area. But specific resistance does not change.