Eddy Currents
When large pieces of conductors are placed in changing magnetic flux, small circulating currents are induced in them.
These currents are called eddy currents because they swirl around in the conductor like eddies in water.
If a peace of metal is placed in a varying magnetic field rotated high speed in a uniform magnatic field ,then induced current setup .the peace are like whire pool of air ,called Eddy currents .
The eddy currents are induced currents in the body of conductor when subjected to changing magnetic flux and this currents are in the pattern of eddiesin the water.
It is also called Foucault current on the name of the scientist Foucault. let Consider an electromagnet when attached to the battery because of the current magnetic field will be produced which will induce current in the metallic plate and current will be in the form of eddies.
The eddy current can be defined as :
Applications
Magnetic braking system in trains:
There are no mechanical linkages, that's why, the braking effect is smooth.
Strong electromagnets are situated above the rails in some electrically powered trains. When the electromagnets are activated, the eddy currents induced in the rails oppose the motion of the train.
Analogue power meters:
The shiny metal disc in the electric power meter rotates due to the eddy currents. Electric currents are induced in the disc by magnetic fields produced by sinusoidally varying currents in a coil.
Electromagnetic damping:
Certain galvanometers have a fixed core made of nonmagnetic metallic material. When coil oscillates, the eddy currents generated in the core oppose the motion and bring the coil to rest quickly.
Induction furnace:
Induction furnace may be used to produce high temperatures and may be utilised to prepare alloys by melting the constituent metals. A high frequency alternating current is passed through a coil which surrounds the metals to be melted. The eddy currents generated in the metals produce high temperatures sufficient to melt it.
Disadvantages of eddy current
a. The eddy current (value) is highly sensitive to the value of permeability. This causes difficulty in the functioning of detectors.
b Heat is lost in the core of transformers due to eddy currents.