Hall effect

Lore & Background

In the 1820s, André-Marie Ampère observed that wires carrying current in a magnetic field experience a mechanical force perpendicular to both the current and magnetic field, an underlying mechanism that led to the discovery of the Hall effect. Edwin Hall explored whether magnetic fields interacted with the conductors or the electric current. He reasoned that if the force acted specifically on the current, it should crowd current to one side of the wire, producing a small measurable voltage. Eighteen years before the electron was discovered, his measurements of the tiny effect were an experimental tour de force, published under the name 'On a New Action of the Magnet on Electric Currents'.

Reader's Guide

The Hall effect is significant because it provides a direct experimental confirmation of the Lorentz force acting on charge carriers in a conductor. The Hall coefficient, defined as the ratio of the induced electric field to the product of the current density and the applied magnetic field, is a characteristic of the material, depending on the type, number, and properties of the charge carriers. This effect allows determination of whether charge carriers are electrons or holes, and their density, which is fundamental to semiconductor physics and the design of Hall-effect sensors. The discovery also validated Maxwell's electromagnetic theory at a time when the electron had not yet been identified, demonstrating that the force on a current-carrying wire is exerted on the moving charges themselves, not on the conductor material. Its legacy includes widespread applications in magnetic field measurement, position sensing, and current monitoring.

Did You Know?

• The Hall voltage arises because moving charge carriers experience a Lorentz force that curves their paths, causing charge accumulation on one face of the conductor.
• The Hall coefficient depends on the type, number, and properties of the charge carriers in the material.
• Hall's discovery was published under the title 'On a New Action of the Magnet on Electric Currents'.