Eddy currents are loops of electric current induced within conductors by a changing magnetic field in the conductor according to Faradays law of induction. They are also induced by the relative motion of a conductor in a magnetic field. Here are some key points about eddy currents:

• Eddy currents are named so because the current looks like eddies or whirlpools.
• The size of the eddy current is proportional to the size of the magnetic field, the area of the loop, and the rate of change of magnetic flux, and inversely proportional to the resistivity of the conductor.
• Eddy currents generate resistive losses that transform some forms of energy, such as kinetic energy, into heat. This Joule heating reduces the efficiency of iron-core transformers and electric motors and other devices that use changing magnetic fields.
• Eddy currents can be used to heat objects in induction heating furnaces and equipment, and to detect cracks and flaws in metal parts using eddy-current testing instruments.
• Eddy currents can also have undesirable effects, such as power loss in transformers. In this application, they are minimized with thin plates, by lamination of conductors, or other details of conductor shape.
• Eddy currents can be removed by cracks or slits in the conductor, which break the circuit and prevent the current loops from circulating. This means that eddy currents can be used to detect defects in materials. This is called nondestructive testing and is often used in airplanes.

In summary, eddy currents are a phenomenon that occurs in conductors when exposed to a changing magnetic field or relative motion in a magnetic field. They can have both desirable and undesirable effects, and are used in various applications such as induction heating and nondestructive testing.