A Hall-effect probe operates with a 120 -mA current. When the probe is placed in a uniform magnetic field of magnitude 0.0780 T, it produces a Hall voltage of 0.740 µV.
(a) When it is used to measure an unknown magnetic field, the Hall voltage is 0.340 µV. What is the magnitude of the unknown field?
.............. mT
(b) The thickness of the probe in the direction of B is 1.60 mm. Find the density of the charge carriers, each of which has charge of magnitude e).
.............. m-3