A Hall-effect probe operates with a 120 -mA current. When the probe is placed in a uniform magnetic field of magnitude 0.0840 T, it produces a Hall voltage of 0.660 µV. The thickness of the probe in the direction of B is 2.00 mm. Find the density of the charge carriers, each of which has charge of magnitude e).
thank you
http://www.jiskha.com/display.cgi?id=1302055271
see the link I gave you....n was the charge density, as I recall.