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CBSE Class 10 Science Exam 2014 Term 1 Paper

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Question : 15
Total: 36
The resistance of a wire of 0.01‌cm radius is 10Ω. If the resistivity of the material of the wire is 50×10−8‌ohm metre, find the length of the wire.
Solution:  
Given : Resistance of a wire, R=10Ω
Radius of wire,
r=0.01‌cm=0.01×10−2m
Resistivity, ρ=50×10−8Ωm
Area of cross-section of wire A,
=πr2=3.14×(0.01×10−2)2
=3.14×0.01×0.01×10−4
=3.14×10−8m2
As,
R‌=ρ‌
l
A

l‌=‌
R×A
ρ
=‌
10×3.14×10−8
50×10−8

‌=0.628m
or
l‌=‌
R×A
ρ
=‌
10×3.14×10−8
50×10−8

‌=0.628m
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