A Hall-effect probe operates with a 121 mA current. When the probe is placed in a uniform magnetic field with a magnitude of 0.0758 T, it produces a...

A Hall-effect probe operates with a 121 mA current. When the probe is placed in a uniform magnetic field with a magnitude of 0.0758 T, it produces a Hall voltage of 0.691 µV. When it is measuring an unknown magnetic field, the Hall voltage is 0.337 µV. What is the unknown magnitude of the field? B.If the thickness of the probe in the direction of B is 1.88 mm, calculate the charge-carrier density (each of charge e).?