CBSE Class 12 Physics 2020 Outside Delhi Set 1 Paper

Question : 22 of 37

Marks: +1, -0

A wire of length

L_0

has a resistance

R_0

. It is gradually stretched till its length becomes

2 L_0

.
(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

2 {\L}_{ {\o}}

Solution:

(a) R vs. L graph :

(b)

\;\text " When length "\;\;=L_0

\;\text " Area "\;\;=A_0

\;\text " Resistance "\;\;=R_0=ρ \;{L_0}/{A_0}

\;\text " When length "\;\;=2 L_0

\;\text " Area "\;\;=\;{A_0}/{2}

\;\text " Then "\; R\;=ρ \;{L}/{A}

\;\text " Or, "\; \;\; R\;=ρ \;{2 L_0}/{A_0 \/ 2}=4 ρ \;{L_0}/{A_0}=4 R_0

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