Overview
Eddy currents are loops of electrical current induced within conductors by a changing magnetic field
in the conductor, according to Faraday's law of induction. They flow in closed loops within conductors,
perpendicular to the magnetic field, and dissipate energy as heat due to the electrical resistance of
the conductor.
Key Points
- Eddy currents are induced by changing magnetic fields
- They flow in closed loops within conductors
- Energy is dissipated as heat (Joule heating)
- Direction follows Lenz's Law (opposes the change)
- Can be minimized by using laminated cores
Theory & Physics
When a conductor moves through a magnetic field, or when the magnetic field through a stationary
conductor changes, an electromotive force (EMF) is induced in the conductor according to Faraday's
Law of Electromagnetic Induction.
Faraday's Law
The induced EMF in any closed circuit is equal to the negative of the time rate of change of the magnetic flux through the circuit.
How Eddy Currents Form
1. A changing magnetic field passes through a conductor
2. This induces an EMF within the conductor
3. Free electrons in the conductor begin to move
4. Currents flow in circular paths (eddies) within the material
5. These currents create their own magnetic field
Lenz's Law
Lenz's Law states that the direction of the induced current will be such that it opposes the change
that produced it. This is a consequence of the conservation of energy.
Important
- The negative sign indicates opposition to the change
- If a magnet approaches, eddy currents repel it
- If a magnet recedes, eddy currents attract it
- This explains magnetic braking and levitation
Real-World Applications
1. Magnetic Braking
Used in roller coasters and trains. A powerful magnet moves past a conductive plate or rail,
inducing eddy currents that create an opposing magnetic field, slowing the vehicle smoothly
without friction or wear.
2. Maglev Trains
Magnetic levitation trains use eddy currents for both levitation and propulsion. The train
floats above the track, eliminating friction and enabling extremely high speeds.
3. Induction Heating
Rapidly alternating magnetic fields induce strong eddy currents in metal objects, heating
them efficiently. Used in induction cooktops and industrial metal processing.
4. Metal Detectors
Eddy currents induced in metallic objects create their own magnetic fields, which are detected
by the sensor, triggering an alert.
Key Equations
Summary
Remember These!
- Eddy currents are induced currents that flow in loops within conductors
- They are caused by changing magnetic fields (Faraday's Law)
- Their direction opposes the change (Lenz's Law)
- They convert kinetic energy to heat energy
- Applications include braking, levitation, and heating
- Laminated cores reduce unwanted eddy currents