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CBSE Class 12 Physics 2020 Outside Delhi Set 1 Paper

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Question : 22
Total: 37
A wire of length L0 has a resistance R0. It is gradually stretched till its length becomes 2L0.
(a) Plot a graph showing variation of its resistance R with its length L during stretching.
(b) What will be its resistance when its length becomes 2Lo ?
Solution:  
(a) R vs. L graph :
(b) ‌ When length ‌‌=L0
‌ Area ‌‌=A0
‌ Resistance ‌‌=R0=ρ‌
L0
A0

‌ When length ‌‌=2L0
‌ Area ‌‌=‌
A0
2

‌ Then ‌R‌=ρ‌
L
A

‌ Or, ‌‌‌R‌=ρ‌
2L0
A0∕2
=4ρ‌
L0
A0
=4R0
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