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CBSE Class 12 Physics 2020 Outside Delhi Set 3 Paper

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Question : 9 of 13
Marks: +1, -0
SECTION - B
A wire of length LoL_o has a resistance R0R_0. It is gradually stretched till its length becomes 1.5Lo1.5 L_o.
(a) Plot the graph showing variation of its resistance RR with its length ll during stretching.
(b) What will be its resistance when its length becomes 1.5Lo1.5 L_o ?
Solution:  
(a) R vs. L graph :
 (b) When length =L0\text{ (b) 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 =1.5L0\text{ When length } = 1.5 L_0
 Area =A01.5\text{ Area } = \frac{A_0}{1.5}
 Then R=ρLA\text{ Then } R = \rho \frac{L}{A}
 Or, =ρ1.5L0A01.5=2.25\text{ Or, } = \rho \frac{1.5 L_0}{\frac{A_0}{1.5}} = 2.25 ρL0A0=2.25R0\rho \frac{L_0}{A_0} = 2.25 R_0
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