QJEEM19Ph7c42: JEE Main 2019 Physics - Class 11 JEEM19Ph7c42 Solution: A copper wire is stretched to make it 0.5% longer. The…

Question

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A copper wire is stretched to make it 0.5% longer. The percentage change in its electrical resistance if its volume remains unchanged is :

Accepted Answer

We know,

R = \frac{ρ l}{A}

and Volume (V) = A

l

\Rightarrow

A

=

\frac{V}{l}

∴

R = \frac{ρ l^{2}}{v}

∴

\frac{Δ R}{R} = 2 \frac{Δ l}{l}

=

2

\times

0.5

=

1%

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