Question

please answer my questions
Answer 2345​

Answer 1

First thing first, resistivity is the intrinsic property of a material which doesn't changes (considering at normal conditions).

The relationship between Resistance R and the Resistivity ρ is

R=ρ×l/A

Where l is the length of the wire and A is its cross sectional area.

Now, taking the logarith and differentiating,

We have

ΔR/R=Δl/l−ΔA/A

Since ρ is constant so it will be eliminated.

Considering no change in the cross sectional area, the equation remains : ΔR/R=Δl/l

Multiply by 100 results in percentage error.

(ΔR/R)×100=(Δl/l)×100

Given is percentage increase in length is 25%

So, (ΔR/R)×100=25

Or percentage increase in resistivity is 25%.

P.s the cross sectional area is considered unchanged here as no information is given about that. However, this is not practical amd it does change on extension of wire.