JEE PYQ: Mathematics In Physics Question 22
Question 22 - 2019 (09 Jan Shift 1)
A copper wire is stretched to make it 0.5% longer. The percentage change in its electrical resistance if its volume remains unchanged is:
(1) 2.0%
(2) 2.5%
(3) 1.0%
(4) 0.5%
Show Answer
Answer: (3)
Solution
Resistance, $R = \frac{\rho l}{A}$ $R = \rho \frac{l \times l}{V} = \frac{\rho l^2}{V}$ $[\because \text{Volume}(V) = Al]$ Since resistivity and volume remains constant therefore % change in resistance $\frac{\Delta R}{R} = \frac{2\Delta l}{l} = 2 \times (0.5) = 1%$
BETA
