Learning Goal: To learn to apply the concept of current density and microscopic Ohm's law.

A slab of metal of volume V is made into a rod of length L . The rod carries current I when the electric field inside is E.

A)Find the resistivity of the metal P.

B)The rod is now stretched so that its length is doubled. If the electric field remains the same, what is the new current I' in the rod?

C)A piece of copper is made into a rod with a square cross-section. The side of the square is 2.00 centimeters. The resistivity of copper is 1.7 *10^-8 om*m. . An unknown electric field E, directed along the rod, creates a current of 12.0 amperes through the rod. Find the magnitude of E.