Q.
A wire of 1Ω has a length of 1 m. It is stretched till its length increases by 25%. The percentage change in resistance to the nearest integer is :
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a
76%
b
12.5%
c
25%
d
56%
answer is D.
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Detailed Solution
R=ρLA=ρL2AL⇒R=ρL2V Stretching does not change volume of wire. ⇒R∝L2⇒R1R2=p2(1.25l)2=11.5625⇒R2=R1[1+0.56]∴ΔRR×100=56%
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