EDDY CURRENTS

INFACT Eddy currents were first observed by Focult. And he says that,
Whenever there is a change in magnetic flux
associated with conductors of irregular shapes,
free electrons in them experience force and
move on the path of least resistance.
For example, consider a circular metal plate falling downwards through a uniform magnetic field applied in a direction going into the plane of paper normally as shown in the figure. Here magnetic field is shown only in a limited part, though it is not necessary to be so. Here free electrons inside the plate also move in the downward direction through the magnetic field and experience force
→      →   →
F = - e v × B . The electrons move on the path that offer minimum resistance and constitute irregular currents called eddy currents. According to Lenz’s law, the direction of these currents is such that the magnetic field produced due to them opposes the motion of the conductor and the plate appears to fall with acceleration less than g.
For this reason, when a pendulum made up of metal plate is allowed to oscillate between two poles of a magnet, it performs damped oscillations. Such a damping is called electromagnetic damping.
Eddy currents result in unwanted joule heat. To avoid it, slots are cut in the conductor as shown in he figure which breaks the current loops. Eddy currents can also be reduced by preparing the conductor from insulated laminae of metal.
Force acting on a metal rod falling in a magnetic field is
F = I B L = B L v / R ) BL This force being directly
proportional to v, the eddy currents are used in preparing braking system in trains to apply brakes smoothly.