What are Eddy Currents?

Have you seen a speedometer inside your vehicle? In the speedometer, a small magnet is connected to the main shaft of the vehicle. According to the speed of the vehicle it rotates. Due to the effects of the eddy currents the motion of the rotating is opposed and the pointer gets deflected through a certain angle. The pointer attached to the calibrated scale indicates the speed of the vehicle.

Induced electromotive force is produced in the coil when there is a change in the magnetic flux linked with that coil. Eddy currents are named so because the current looks like eddies or whirlpools. When a conductor is placed in the changing magnetic field, the induced current in the conductor is termed as Eddy currents.

 

Eddy currents

Like Lenz’s law, there are lots of experiments done to explain the eddy currents. The first test showed that inside a solenoid a soft iron core is introduced and it is connected to the alternating electromotive force. When the metallic disc is placed over the soft iron core, the circuit is switched on and when the circuit is turned on the metallic disc is thrown up away from the iron core.

Primarily, eddy currents will be introduced in the material, when an electrically conductive material is placed in the coils magnetic field an electromagnetic induction occurs.

The magnitude of the eddy currents produces large current since the resistance of the metallic conductor becomes low. They may produce undesirable effects if the large eddy current is allowed to in the core of a choke coil, transformer, etc.

By making use of a laminated core, the eddy currents produced in the core of a transformer are reduced. In present days, electric brakes are provided in the trains in addition to those vacuum brakes.

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Practise This Question

The pointer of a dead-beat galvanometer gives a steady deflection because [MP PMT 1994]