Charges move at speed v across a conductor of width l, with B, v and l mutually perpendicular. What is the Hall emf?

1. Charge separation continues until the electric force balances the magnetic force, so qE = qvB. 2. Cancelling q gives E = vB for the electric field across the conductor. 3. For a uniform field, E is the voltage divided by the width, so emf/l = vB. 4. Multiplying both sides by l gives emf = Blv. 5. The Hall emf therefore grows with field, width and speed, which is why a wide pipe gives a larger reading than a narrow one. _Source: OpenStax College Physics (CC BY 4.0), Ch 22 "Magnetism", section 22.6 The Hall Effect_