- #1
Abdulwahab Hajar
- 56
- 2
Homework Statement
A long round wire of radius a and conductivity σ is coated with a material of conductivity 0.1σ. (a) What must be the thickness of the coating so that the resistance per unit length of the uncoated wire is reduced by 50%?
2. Homework Equations [/B]
R = l/(σS)
where R is the resistance, l is the length of the wire, σ the conductivity and S the cross sectional area
The Attempt at a Solution
regarding part a) the resistance per unit length of the uncoated wire is (1/σS) this equals 1/(σπa2
meaning that its resistance per unit length doesn't depend on the thickness of the coating.
However the soln manual
solved it by setting: resistance per unit length of coated wire = resistance per unit length of uncoated wire
Why is that so??