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JEE Main 2019 (9 Jan, Shift 1) · Ohm's Law, Resistivity & Temperature

Ohm's Law, Resistivity & Temperature question from JEE Main 2019 (9 Jan, Shift 1)

Q47JEE Main 2019 · 9 JAN · SHIFT 1Medium

Ohm's Law, Resistivity & Temperature

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

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Answer: (c)

Volume constant, so $R \propto l^2 \Rightarrow \dfrac{\Delta R}{R} = 2\dfrac{\Delta l}{l}$ for small changes.
$\Delta R/R = 2\times0.5\% = 1\%$ . The answer is (c).

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