The Hall effect is the creation of a potential difference perpendicular to both the current flow in a conductor and the magnetic field which pass it. The Hall effect was discovered in 1879 by Edwin Hall, an American physicist. It has many applications such as measuring current and fluid flows.

How the Hall Effect Works

The charge carriers moving through the magnetic field are subjected to Lorentz force that deflect them away perpendicular to their normal path. This separation of charge carriers creates a potential difference between the opposite edges. The electric field created by this separation balances the buildup of further charge, resulting in a steady voltage while the current is flowing and the magnetic field is present. The size of the voltage depends on the current, magnetic field strength, material thickness, and it's charge carrier density.

The Hall coefficient, also called the Hall constant, is a material property related to the density of it's mobile charge carriers. It is used to calculate the voltage created for a given current, magnetic field, and thickness.

Semiconductors are more complicated than metals because they have positive and negative charge carriers, called holes and electrons respectively. Calculating the Hall effect is also more difficult than for metals.

Hall Effect Applications

Hall effect sensors are used in meters that detect current flow without making contact with the conductor. They are especially useful for measuring small direct currents which do not induced enough current to be measured accurately by other clamp meters. Hall effect sensors are also used to detect detect fluid flow in pipes, and they are used in electronic compasses to calculate bearings relative to the Earth's magnetic field.

Equipment that must operate in harsh environments use Hall sensors because they have no moving parts, or parts that need to stay clean. They are more robust than mechanical or optical sensors which suffer from dust and water, and need to be cleaned regularly.

Hall effect sensors are used extensively in cars and trucks. They are used instead of mechanical breaker points for timing in modern ignition systems. They are used in anti-lock braking systems to detect when the wheels have stopped moving. They are also used with other sensors to measure the amount of skidding, allowing the drive control to compensate.