Answer 1—Bulk resistivity is defined as the E field (volts/meter) required to achieve a given current density (amperes/meter²). If you write this out and then cancel the units, you get the following:

Another way to think of it is to imagine a rectangular block of material that has conductive end caps on opposite faces. The total resistance is going to be proportional to the length of the block between the caps, and inversely proportional to the area (length²) of the caps. You can write this out as the following equation: 

 Solving for resistivity and canceling units where possible gives you: 

Contributor: David Tweed