Hall Probes

Overview

This lesson explains the Hall effect and how Hall probes measure magnetic flux density. You will connect magnetic force on charge carriers to a measurable transverse voltage.

What You Need to Know

• Moving charge carriers in a magnetic field experience a sideways magnetic force.
• Charge builds up on opposite sides of the conductor until the electric force balances the magnetic force.
• This separation produces a Hall voltage.
• The Hall voltage is given by VH = BI / (ntq), where n is number density, t is thickness, and q is the charge of each carrier.
• A Hall probe uses a calibrated Hall voltage to measure magnetic flux density.

How to Work Through It

1. Draw the conductor, current direction, magnetic field, and sideways force.
2. Explain how charge separation creates an opposing electric field.
3. Use the balanced-force derivation to reach VH = BI / (ntq).
4. Practise using the equation and interpreting Hall probe readings.

Check Your Understanding

• Why does the Hall voltage stop increasing once equilibrium is reached?
• How does increasing current affect Hall voltage?
• Why are semiconductors useful in Hall probes?
• What happens to the sign of the Hall voltage if the charge carriers change sign?

Common Mistakes

• Confusing conductor thickness t with the length of the sample.
• Treating number density n as the number of charge carriers rather than carriers per unit volume.
• Forgetting that the Hall voltage is across the sample, not along the current direction.
• Ignoring the sign of the charge carrier when reasoning about polarity.

Next Steps

• Use Hall probe ideas to interpret magnetic field measurements in later induction work.
• Keep the moving-charge force model secure.