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A wire of resistance 6 ohm and length 20 cm is stretched to length 60 cm. Assuming that it has a uniform cross section , what will be its new resistance.
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12th
Physics
Current Electricity
Electrical Resistance & Resistivity
A wire of 3 ohm resistance ...
PHYSICS
A wire of 3 ohm resistance and 10 cm length is stretched to 30 cm length. Assuming that it has a uniform cross section, what will be its new resistance?
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ANSWER
On stretching a wire, both its area of cross-section and length changes but its volume remains constant.
R
1
=3Ω , l
1
=10cm , l
2
=30cm=3l
1
And, A=
l
V
Now, R=ρ
A
l
⟹R=ρ
V
l
2
⟹R∝l
2
On increasing length to 3 times of initial value.
Hence,
R
1
R
2
=
l
1
2
l
2
2
=9
⟹R
2
=9R
1
=9×3Ω
R
2
=27Ω
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