Question

What do you mean by eddy current? How does it affect the energy losses? Write the uses of eddy current.

Hint:

Eddy currents are induced circulating currents in bulk conductors due to changing flux; they cause \(I^2R\) heating (reduced by laminated cores) and are used in induction furnaces and electromagnetic braking.

Answer 1

Step 1: Definition of eddy current.
When the magnetic flux linked with a solid (bulk) piece of conductor changes with time, induced currents are set up inside the body of the conductor. These induced currents flow in closed loops that look like swirling whirlpools of water, and are called eddy currents (also Foucault currents). They obey Lenz's law, so they oppose the change in flux that produces them.

Step 2: Effect on energy losses.
Eddy currents flow through the resistance of the conductor and dissipate energy as heat (\(I^2R\) loss). In devices like transformer cores, motors and generators this heating is an unwanted energy loss that lowers efficiency and heats up the core.

Step 3: How the loss is reduced.
To minimise eddy-current loss, the core is made of thin laminated sheets insulated from one another (by varnish/oxide layers), and materials of high resistivity (like silicon steel) are used. Lamination breaks the large eddy-current loops into many small high-resistance loops, greatly reducing the current and hence the heat produced.

Step 4: Useful applications of eddy currents.
Although often a nuisance, eddy currents are put to good use in:
(i) Induction furnace for melting metals.
(ii) Electromagnetic (eddy-current) braking in trains and moving vehicles.
(iii) Induction motor operation.
(iv) Dead-beat galvanometer, where eddy currents quickly bring the needle to rest.
(v) Speedometers and energy (electric) meters.
(vi) Induction cook-tops for heating.
\[\boxed{\text{Eddy currents} = \text{induced whirlpool currents in bulk conductors; cause } I^2R \text{ heating; reduced by lamination}}\]