When 0.81 m of a wire with cross-sectional area of 3.1*10^-11 m^2 is connected across a 2 V battery a current of 1.6 A flows in the wire. Find the resistivity of the material of the wire.

The resistance in the wire is given by the resistivity of the material by the lenght and divided by the cross-sectional area (R = pL/A). From here we can rearrange and have p = RA/L. However, we also know that R = V/I, and thus, our final formula becomes p = VA / IL. Plugging in the numbers we get p = 23.110^-11 / 1.60.81, which is equal to 4.7839510^-11, or rounding, 4.8*10^-11 Ohm-meters.