Question

If length of wire is 2unit and area of cross section is 1 unit, what is the resistivity?

Answer 1

Answer:

The Resistivity of the wire will not change with the change in length. Resistivity is a property of the wire, it doesn't depend upon it’s length or cross-sectional area.

However, If you are asking about Resistance, it will increase to 4 times it’s initial value.

Resistance,R = ρl/A

Where,

ρ=Resistivity of the wire

l=lenght of wire

A= cross section of the wire

So, now if you increase the length of wire by 2 times it’s cross-sectional area will decrease by 2 times, because the volume of the wire has to remain constant.

Let, the initial and final radius of the wire be r1,&r2 respectively.

Since the initial and final volume are equal, so

2π(r1^2)l = 2π(r2^2)(2l)

So, r2=r1/√2

So, the cross-sectional area becomes 1/2 times the initial value.

Putting the values in the formula for resistance, we get the new resistance 4 times greater than the initial vakuev of resistance.

Answer 2

$\huge\rm{\orange{\underline{\underline{Answer→}}}}$

R=

A

ρl

⇒A=

R

ρl

⇒A=

46

1.84×10

−6

×2

⇒A=8×10

−8

m

2