Question

A piece of wire of resistance 20 ohm is drawn out so its length is increased to twice its original length. Calculate the resistance of wire in yhe new situation.

Answer 1

Now the resistance will be 40 ohm

Answer 2

Given resistance , R = 20 Ω

And we have to find the new resistance with the help of the original length .

Solution :

We know very well that ,

R = (pl/A)

We can write it as :

R = (pl²/v)

Then ,

It is given that

l' = 2l

So ,

R' = (4pl²)/V = 4R ----(eq.1)

R = 20 ohm = 20 Ω

So , putting R = 20 ohm in equation 1 ,

We have :

R' = 4R = 4(20) = 80 Ω

The required new resistance is of 80 ohm = 80Ω