Question:

Use of eddy currents is done in the following except

Updated On: Jul 2, 2022
  • moving coil galvanometer
  • electric brakes
  • induction motor
  • dynamo
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The Correct Option is D

Solution and Explanation

Eddy currents are currents induced in the body of a conductor due to change in magnetic flux linked with the conductor. When a steady current is passed through the coil of a galvanometer it is deflected. Normally, the coil oscillates about its equilibrium position for some time before coming to rest. To avoid delay due to these oscillations, the coil is wound over a metallic frame. As the coil is deflected, eddy currents set up in the metallic frame oppose its motion. Eddy currents are used in controlling the speed of electric trains. A strong magnetic field is applied to a metallic drum rotating with the axle connecting the wheels. Large eddy currents set up in the rotating drum oppose the motion of the drum and tend to stop the train. An induction motor or AC motor is also based on application of eddy currents. Dynamo is not based on application of eddy currents.
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Concepts Used:

Eddy Currents - Induction Furnace

Eddy currents are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday’s law of induction. Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field.

Some of the uses of the eddy current are as follows:

  1. Automobile speedometers: Eddy currents are used to know the speed of a vehicle. A speedometer consists of a rotating magnet, which rotates based on the speed of the vehicle, producing Eddy Current in the drum. When the drum turns in the direction of the rotating magnet, the pointer attached to the drum indicates the speed of the vehicle. 
  2. Magnetic brakes: When you press the brakes, the metal wheels get exposed to a magnetic field which generates eddy currents in the wheels. The interaction between the eddy currents and the applied magnetic field slows the wheels down. 
  3. Energy meters: A metal disc in the electric power meter rotates due to eddy currents. The magnetic field induces the electric currents in the disc by alternating varying currents in a coil. 
  4. In induction furnaces: Eddy current is used for a uniform increase of temperatures in induction furnaces. Large eddy currents start flowing in rapidly changing magnetic fields, due to a large emf being produced. This produces high temperatures. A coil is wound over a constituent metal, placed in a highly oscillating magnetic field, produced by high frequency.
  5. Free-fall devices (detecting coins in vending machines): Eddy current helps detect counterfeit coins and notes in vending machines. Eddy currents slow down the speed of the coins as they move past a stationary magnet. 
  6. Galvanometers (a device that measures small electrical currents): Eddy current is set up in the galvanometer by an oscillating coil, and its resistive forces oppose further oscillations of the coil. This enables the coil to quickly attain its equilibrium position.
  7. Proximity/displacement sensors
  8. Induction alternating current (AC) motors