CBSE Class 12 Physics 2020 Outside Delhi Set 3 Paper

Question : 9 of 13

Marks: +1, -0

SECTION - B

A wire of length

L_o

has a resistance

R_0

. It is gradually stretched till its length becomes

1.5 {\L}_{ {\o}}

.
(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

1.5 {\L}_{ {\o}}

Solution:

(a) R vs. L graph :

\;\text " (b) When length "\;\;=L_0

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

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

\;\text " When length "\;\;=1.5 L_0

\;\text " Area "\;\;=\;{A_0}/{1.5}

\;\text " Then "\; R\;=ρ \;{L}/{A}

\;\text " Or, "\; \;\; =ρ \;{1.5 L_0}/{A_0 \/ 1.5}=2.25

ρ \;{L_0}/{A_0}=2.25 R_0

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