Physics current problem?

Question

The electric field in a 2.0 mmX 2.0 mm square aluminum wire is 0.0012 N/C. What is the current in the wire?

Answer 1

You need to look up the resistivity of aluminum to solve the problem. Call it r, for now, and assume it's measured in ohm-mm to match your units (but you will probably have to convert it from some other units like ohm-m or ohm-cm).

They don't tell you how long the wire is, but I think it's easiest to solve this problem by considering what happens in some piece of the wire of length L.

The potential difference V over a distance L with constant electric field strength E parallel to that length is:
V = E*L

The resistance of a conductor with resistivity r, uniform cross sectional area A, and a length L is:
R = r*L/A

Finally, the definition of resistance (R=V/i) gives:
i = V/R = E*L / (r*L/A) = E*A/r

Not that the length L does not appear in the final answer.