Test: Eddy Currents(21 Dec) - JEE MCQ

• The iron core of a transformer is made of Laminated silicon steel with special insulated coating to limit Eddy current loss.
• Electrical steel, also called lamination steel is specialty steel tailored to produce certain magnetic properties, such as a small hysteresis area (small energy dissipation per cycle, or low core loss) and high permeability.
  

Eddy current when produced it causes damping heat loss energy loss but it don't produce any type of sparking because the electrons are only at the surface of the conductor and the electrons do not jump off to enter the air and heat it. 

• Eddy currents are the currents which are induced in a conductor whenever the amount of linked magnetic flux with the conductor changes.
• These were discovered by Foucault in the year 1895 and hence they are also called Foucault currents.

Eddy currents:

• When a conductive material is subjected to a time-varying magnetic flux, eddy currents are generated in the conductor.
• These eddy currents circulate inside the conductor generating a magnetic field of opposite polarity as the applied magnetic field. The interaction of the two magnetic fields causes a force that resists the change in magnetic flux.
• However, due to the internal resistance of the conductive material, the eddy currents will be dissipated into heat and the force will die out. As the eddy currents are dissipated, energy is removed from the system, thus producing a damping effect.

• The no load current is about 2-5% of the full load current and it accounts for the losses in a transformer.
• These no-load losses include core(iron/fixed) losses, which contains eddy current losses & hysteresis losses and the copper (I²R) losses due to the no Load current.

• Stronger magnetic field, thicker material and low resistivity material will increase the size and effect of eddy current whereas thinner material will reduce the effect of eddy currents.

• It is induced EMF of periodic EMI, So formula is:

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Here w is angular speed.

Although eddy currents are undesirable, still they find applications in the following devices:

• Induction furnaces
• Electromagnetic damping
• Electric brakes
• Speedometers
• Induction motor
• Electromagnetic shielding
• Energy meters

In electromagnetic induction, line integral of induced field E around a close path is non zero, and induced electric field is non conservative.

• Eddy currents are the currents induced in solid masses when the magnetic flux threading through them changes.
• Eddy currents also oppose the change in magnetic flux, so their direction is given by Lenz’s law.