Ahall probe serves to measure magnetic field strength. such a probe consists of a poor conductor 0.155 mm thick, whose charge-carrier density is 1.05 × 1025 m3. when a 2.67-a current flows through the probe, the hall voltage is measured to be 4.89 mv. what is the magnetic field strength?

We are given the following:
thickness, T = 0.155 mm
charge-carrier density, n = 1.05 x 10^25 / m3
current, I = 2.67 A
voltage, V = 4.89 mV

We are asked to get the magnetic strength, B

To solve this, we use the Hall Effect formula:
V = - IB / neT
where e is the charge of an electron which is e = 1.60 x 10^-19 and B is the magnetic field
Rearranging the formula
B = -V n e T / I
Substituting the given values
B = - (4.89 x 10^-3 V) (1.05 x 10^25 / m3) (0.155 x 10^-3 m) / 2.67 A
B = -2.98 x 10^18 Teslas