Question

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

Answer 1

Explanation:

The length is doubled so the area of area of cross section becomes half

Answer 2

Answer:

R' = 80 ohm

Explanation:

Let the first resistance be R = pl / A ----------(1)

                   new length, l' = 2l

                   l' / l =2

                  the volume will be same

                           V = V'

                        Al = A'l'

                        A'/A = l / l'

                        A'/A = 1/2

                      R ' = pl'/A'---------(2)

       Now divide (2) by (1),

             R'/R = (pl'/ A' ) / (pl/A)

             R' / 20       = 4

                    R' = 80 ohm