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A wire of length l and resistance of R is stretched so that its length is doubled and area of cross section is halved.How will its resistance changes and

its resistivity changes?


Its resistivity is halved if the length is doubled and it also gets half when area is halved....and the resistance is doubled if the length is doubled and it also gets double when area gets halved
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R = ρ L / A

ρ is constant for a material.  It is a property of a substance and it does not change.

Volume of the wire is a constant.  A' = A / 2  and   L' = 2 L
 R' = ρ (2L) / (A/2)
     = 4 * ρ L / A
     =  4 R

the resistance becomes 4 times.

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