Test: Eddy Currents - 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.

Aluminium is used as a coil which is a good conductor.
Dead beat galvanometer:

• Eddy currents are the currents induced in a metallic plate when it is kept in a time varying magnetic field. Magnetic flux linked with the plate changes and so the induced current is set up. Eddy currents are sometimes so strong, that metallic plate become red hot.
• Induction motor, the eddy currents may be used to rotate the rotor. When a metallic cylinder(or rotor) is placed in a rotating magnetic field , eddy currents are produced in it. According to Lenz's law, these currents tends to reduce to relative motion between the cylinder and the field. The cylinder, therefore, begins to rotate in the direction in the field. This is the principle of induction motion.

Eddy currents are produced by varying magnetic field in solid plates, blocks and wires.

Eddy currents are loops of electrical current induced within conductors by a changing magnetic field in the conductor, due to Faraday's law of induction.

• Eddy currents are the currents induced in solid metallic masses when the magnetic flux threading through them changes.
• These currents look like eddies or whirlpools in water and so they are known as eddy currents.

• The electromagnetic damping can be increased by winding the coil on a lighter copper or aluminium frame.
• As the frame moves in the magnetic field, eddy currents are set up in the frame which resists the motion of the coil.