First slide
Ohm's law

wire of resistance 4Ω is stretched to twice its original length. The resistance of stretched wire would be


Resistance of a wire,

R=ρ1A=4Ω         i

When wire is stretched twice, its new length be ‘l’. Then l'=2l

On stretching volume of the wire remains constant.

  lA=l'A'where A'  is the new cross-sectional area Or A'=1l'A=12lA=A2

 Resistance of a stretched wire is R'=ρl'A'=ρ2lA/2=4ρlA

=44Ω=16Ω                                     Usingi

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