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CBSE Class 12 Physics 2020 Outside Delhi Set 3 Paper

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Question : 9
Total: 13
SECTION - B
A wire of length Lo has a resistance R0. It is gradually stretched till its length becomes 1.5Lo.
(a) Plot the graph showing variation of its resistance R with its length l during stretching.
(b) What will be its resistance when its length becomes 1.5Lo ?
Solution:  
(a) R vs. L graph :

‌ (b) When length ‌‌=L0
‌ Area ‌‌=A0
‌ Resistance ‌‌=R0=ρ‌
L0
A0
‌ When length ‌‌=1.5L0
‌ Area ‌‌=‌
A0
1.5
‌ Then ‌R‌=ρ‌
L
A
‌ Or, ‌‌‌=ρ‌
1.5L0
A0∕1.5
=2.25 ρ‌
L0
A0
=2.25R0
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