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CBSE Class 12 Physics 2020 Outside Delhi Set 1 Paper

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Question : 22 of 37
Marks: +1, -0
A wire of length L0L_0 has a resistance R0R_0. It is gradually stretched till its length becomes 2L02 L_0.
(a) Plot a graph showing variation of its resistance RR with its length LL during stretching.
(b) What will be its resistance when its length becomes 2Lo2 L_{o} ?
Solution:  
(a) R vs. L graph :
(b)  When length =L0\text{ When length } = L_0
 Area =A0\text{ Area } = A_0
 Resistance =R0=ρL0A0\text{ Resistance } = R_0 = \rho \frac{L_0}{A_0}
 When length =2L0\text{ When length } = 2 L_0
 Area =A02\text{ Area } = \frac{A_0}{2}
 Then R=ρLA\text{ Then } R = \rho \frac{L}{A}
 Or, R=ρ2L0A02=4ρL0A0=4R0\text{ Or, } R = \rho \frac{2 L_0}{\frac{A_0}{2}} = 4 \rho \frac{L_0}{A_0} = 4 R_0
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