Question

A piece of wire is redrawn by pulling it until its length is doubled. Compare the new resistance with the original resistance?​

Answer 1

Explanation:

Volume of the material of wire remains same. So, when length is doubled its area of cross-section will get halfed.

So, if l & a are the original length & area of cross-section of the wire,

0riginal value of Resistance,

R = p × l / a

New value of Resistance,

R' = p × 2l / a/2

  = p l/a × 4

  = 4R

Answer 2

Answer:

Since, the volume should remain conserved.

Now

R1=pl1/A1

If the length is doubled so, the length becomes 2l1=l2

So, by volume conservation

l1A1=l2A2

l1A1=2l1A2

So,A2=A1/2

Now R2=p×2l1/A1/2

R2=4R1

Hence the new resistance increase by 4 times.

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