Using a Hall Probe | CAIE 9702 Paper 4 Notes

Paper 4

Physics9702

Using a Hall Probe

A calibrated Hall voltage can be used to measure magnetic flux density.

How the probe responds

For a fixed probe and current, Hall voltage is proportional to B.
The reading is maximum when the field is perpendicular to the large face and zero when it is parallel (9702/42/F/M/23 Q6(a)).
A semiconductor gives a larger voltage because its carrier number density is smaller. A thinner slice also increases the voltage.

Worked example

A Hall-probe reading

A probe has B = 4.0 μT, I = 5.4 A, n = 1.5 × 10¹⁶ m⁻³ and t = 1.8 mm. Find the Hall voltage (9702/42/O/N/23 Q7(a)).

V_{\mathrm H}=\dfrac{BI}{ntq}

V_{\mathrm H}=5.0\ \mathrm{V}

Answer

V_{\mathrm H}=5.0\ \mathrm{V}

Your turnquick check

For the same field and current, what happens to Hall voltage when the slice thickness is halved?

Show worked answer

The Hall voltage doubles because it is inversely proportional to thickness.

Common mistake

Hall voltage follows B itself. Induced e.m.f. in the next chapter depends on how quickly magnetic flux changes.