Question

A piece of wire of resistance 20 ohms is drawn out so that its length is increased to twice its original length calculate the resistance of the wire in the new situation

Answer 1

Given,

R=20 Ω  

Let,Length of wire is L and when it drawn out, its new length is 2L

The volume of wire in both the situations remains constant.So, it the length of wire doubled, the area of cross section of wire becomes half.

So, the new resistance of wire-

Rnew = 2l/(A/2)

=4L/A

=4×Old resistance of wire           (Because, R=L/A)

=4×20 = 80 Ω

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Answer 2

As we know that

Resistance is directly proportional to the length of wire