Eddy Currents

What is Eddy Current?

Eddy current is an induced current circulating in any solid conducting body (solid conductive material) in a magnetic field.

When a metal plate (disc or sheet) is allowed to rotate or swing between the poles of a powerful magnet, the induced current flows through the metal plate in such a way that it tends to reduce or resist the motion of the metal plate producing it.  

Eddy current acts as a breaking force because it slows down the movement and motion of a metal plate or disc in a magnetic field. This slowing down of the motion of a disc is called the damping effect of eddy currents.

How to Minimize Energy Loss Through Eddy Current:

When a solid disc rotates in the magnetic field, the current is large and the disc is quickly brought to rest due to the large opposing force provided by the eddy currents.

To minimize energy loss through eddy current:

Use laminated sheets which are made up of thin sheets of metal insulated from each other, i.e cut into slots: If the disc is replaced with a disc containing slots made of insulated metal sheets, the slots increase the resistance of the disc which decreases eddy currents, allowing it to turn in the magnetic field for a longer time. The slots reduce the surface area where eddy currents can flow.

Uses of Eddy Current:

• Damping of galvanometer – to control movement of pointers in moving coil meters.
• Induction cookers or furnaces to melt large amounts of precious metals.
• Used for detecting invisible cracks in railroads which can endanger life.

Disadvantages of Eddy Current:

• Eddy current generates heat in the cores of transformers, and the armature of electric motors and generators.
• It also causes losses of energy and power.
• It reduces the efficiency of transformers, motors and generators.