Iwhat is the resistance of a. a 1.0-m-long copper wire that is 0.50 mm in diameter? b. a i 0-cm-long piece of iron with a 1.0 mm x 1.0 mm square cross section?

The resistance of a conductor is given by:

where
is the resistivity of the material
L is the length of the conductor
A is its cross-sectional area

We can use this formula to solve both parts of the problem.

a) The length of the copper wire is L=1.0 m. Its diameter is d=0.50 mm, so its radius is 

And its cross-sectional area is

The copper resistivity is , therefore the resistance of this piece of wire is


b) The length of this piece of iron is L=10 cm=0.10 m. Its cross-sectional size is L=1.0 mm=0.001 m, so its cross-sectional area is

The iron resistivity is , therefore the resistance of this piece of wire is