Question

An aluminium wire is stretched to make its length, 0.4% larger. The percentage change in resistance is

• A. 0.4%
• B. 0.2%
• C. 0.8%
• D. 0.6%

Answer 1

Answer: (C)

0.8%

Answer 2

When the wire is stretched, volume remains constant. If length is increased by 0.4% area will decrease by 0.4%.
From, $R=\frac {ρI}{A}$

$\frac {dR}{R}\times 100=\frac {dI}{I}\times100+\frac {dA}{A}\times 100$
The percentage change in resistance,
%$R$_ _ =$0.4 + 0.4$
%$R$= $0.8$%

So, the correct option is (C): $0.8$%