Eddy currents : Applications
Electromagnetic brakes –To control the speed of fast moving electric trains.
In case of fast moving trains,on the tracks, magnets are placed so that currents are induced on the wheels of the train.
Electromagnetic brakes do not need any maintenance. It is very economical alternative to friction brakes.
- Consider a very big magnet is placed near the track on which train will go.
- Outer rim of the wheel is coated with copper.
- When the wheel comes near the magnetic field it will experience the magnetic field produced by the magnet.
- This will result in change in flux and induced current will be produced.
- The direction will be given by Lenz’s law.The induced field will give rise to repulsiveinduced field at the boundary.As a result the train slows down a little.
- When the train moves to other end of the magnet it will experience an attractive force because of induced current in the opposite direction.
- Train gradually slows down and finally comes to rest.
- The kinetic energy lost by the train = the heat gained by the copper.
- It obeys the law of conservation of energy.
Electromagnetic damping:- Electromagnetic damping in galvanometers helps to reduce oscillations around equilibrium positions.
- Galvanometers are the instruments which help in measuring currents.
- When the current passes through the galvanometer there is a needle(needle is like a small metal plate) which oscillate after some time it comes to rest.
- Because of electromagnetic dampingneedle comes to rest quickly.As a result magnitude of current can be detected.
- It is same as metal plate entering the magnetic field there is a current induced similarly when leaving the magnetic field there is a current induced.
- The current entering and leaving are in opposite directions.
- These eddy currents oppose the relative motion as a result electromagnetic damping occurs.