Saturday, 28 December 2019

What is Eddy Current? - Applications - Formula- With Experiement

  Daman       Saturday, 28 December 2019

What is Eddy Current?

The word Eddie literally means a circular current. let us now try to understand how they are produced. Take a solenoid that has a soft iron core. Now connect this solenoid to an AC source. When a metallic disc is held over the cross-sectional face of the soft iron core the metallic disc will be thrown into the air.


How does this happen?

Current flows through the solenoid. Hence, magnetic flux linked with the solenoid increases from zero to finite value. This change in magnetic flux gives rise to induced currents in the disk. The upper phase of the soft iron core attains the same polarity as the lower phase of the disk.

Hence the disk is repelled by the soft iron core and is thrown up in the air.

This experiment shows that when a conductor is kept in a changing magnetic field currents are induced in the body of the conductor.

These are currents that occur in very small loops and are called eddy currents. Foucault discovered this concept in 1895.

  • In some cases, these may produce undesirable effects. For example, they increase the internal energy and therefore can increase the temperature of the material. For this reason devices like transformers which are constantly subjected to changing magnetic field are often laminated or their metallic core is divided into thin sheets. Each of these sheets is insulated from one another.
                             
The magnitude of eddy current is given:
                                                       
The direction is given by the lens's law or Fleming's right-hand rule. 
  • Lenz's law states that the direction of induced current is such as to oppose the very cause producing it.
  • Fleming's right-hand rule stretch the forefinger the middle finger and the thumb of the right hand such that they are mutually perpendicular to each other.
                                          

 If the forefinger indicates the direction of the magnetic field the thumb medicates the direction of motion of the conductor, then the middle finger indicates the direction of induced current in the conductor.


Eddy Current Applications

Eddy currents are useful in many ways.
  • One of the applications is electromagnetic damping. When a steady current is passed through the coil of a galvanometer it gets deflected. The coil keeps oscillating for a long time before coming to rest. Since the coil is bound over a metallic frame the eddy currents are set up in the metallic frame. These counts oppose the motion and the call attains its equilibrium position almost instantaneously.
  • The shiny metal disk in the electric power company meter outside your house rotates as a result of eddy current.
  • Eddy currents are induced in the discs by magnetic fields caused by sinusoidally wearing guns in the coil.
  • The metal detectors used at airport security checkpoints operate by detecting eddy currents induced in metallic objects. The metal detector at an airport security checkpoint generates an alternating magnetic field. This magnetic field induces eddy currents in any conducting metal objects carried through the detector. These eddy currents, in turn, produce an alternating magnetic field. This current induces a current in the receiver coil which in turn produces a Beep.

 The eddy current produces undesirable effect in certain cases. For example, these are s produced due to change in magnetic flux heat up the coils. This results in varying tear of the coils.

This is whole about the Basic of What is Eddy Current and Eddy Current Applications.
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