Eddy Currents: Definition, Explanation and Applications

An eddy current is a current originating in an exceeding conductor in response to a changing magnetic field. They flow in closed loops in an exceedingly plane perpendicular to the magnetic field. By Lenz law, this current swirls in such the simplest way as to produce a magnetic field opposing the change; for this to occur in an exceeding conductor, electrons swirl in an exceedingly plane perpendicular to the magnetic field. This effect was discovered in 1819-1868 by physicist Foucault and these currents are called eddy currents.

Have you seen a speed indicator within your vehicle? In the speed indicator, a tiny low magnet is connected to the main shaft of the vehicle. According to the speed of the vehicle, it rotates. Because of the effects of the eddy currents, the motion of the rotating is opposed and also the pointer gets deflected through a precise angle. The pointer hooked up to the calibrated scale indicates the speed of the vehicle. Because of the tendency of eddy currents to oppose, eddy currents cause a loss of energy. Eddy currents remodel a lot of useful kinds of energy, like kinetic energy, into heat, that isn’t usually useful. 

Read Also: Magnetic Properties of Material

Keyterms: Lenz law, Magnetic Field, Electron, Electric power Meters, Speedometers, Induction Chamber, Electromagnetic damping

Read More: Electric Current and Circuit 

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Eddy Current – Explained

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An induced electrical phenomenon is made within the coil once there's a change within the magnetic flux linked with that coil. Eddy currents are named this because the current looks like eddies or whirlpools. Once a conductor is placed within the changing magnetic field, the iatrogenic current within the conductor is termed as Eddy currents. We can outline it as: Eddy currents are loops of electrical current evoked inside conductors by a changing magnetic field within the conductor according to Faraday’s law of induction. Eddy currents flow in closed loops inside conductors, in planes perpendicular to the magnetic field.

Eddy Current

Like Lenz’s law, there are voluminous experiments done to clarify the eddy currents. The first is that, within a solenoid a soft iron core is introduced and it's connected to the alternating electromotive force. Once the metal-like disc is placed over the soft iron core, the circuit is switched on and once the circuit is turned on the metallic disc is thrown up far away from the iron core.
Primarily, eddy currents will be introduced within the material, once conductive electrically semiconducting material is placed within the coils magnetic field an electromagnetic induction takes place.

The magnitude of the eddy currents produces an outsized current since the resistance of the metal-like conductor becomes low. They will produce undesirable effects if the massive eddy current is allowed into the core of a choke coil, transformer, etc.

By making use of a laminated core, the eddy currents made within the core of a transformer are reduced. Within the day, electrical brakes are provided on the trains additionally to those vacuum brakes.

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Practical Application-

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Eddy currents are used to advantage in certain applications like:

• In The Brakes of Trains-

During braking, the brakes expose the metal wheels to a magnetic field that generates eddy currents within the wheels. The magnetic interaction between the applied field and therefore the eddy currents acts to slow the wheels down. The quicker the wheels spin, the stronger is the impact, which means that as the train slows the braking force is reduces, generating a smooth stopping motion. 

• Electromagnetic damping-

Used to design deadbeat galvanometers. Usually, the needle oscillates a bit regarding its equilibrium position before it comes to rest. This causes a delay in taking the reading thus to avoid this delay, the coil is wound over a non-magnetic metal like frame. Because the coil is deflected, eddy currents originate within the set up frame and so, the needle comes to rest nearly instantly.

Thus, the motion of the “coil is damped”. Certain galvanometers have a fixed core created from nonmagnetic metallic material. Once the coil oscillates, the eddy currents that generate within the core oppose the motion and bring the coil to rest.

• Electric Power Meters-

The shiny metal disc within the meter rotates due to eddy currents. The magnetic field induces the electrical currents within the disc. You can additionally observe the shiny disc at your house.

• Induction chamber-

In ever-changing dynamic magnetic fields, because of an outsized voltage created, giant eddy currents are originated. Eddy currents produce temperature. So an outsized temperature is formed. Therefore a coil is wound over a constituent metal that is placed in a field of the extremely oscillating magnetic field created by high frequency. The temperature created is enough to soften the metal. This is often used to extract metals from ores. Induction chamber are often used to prepare alloys, by melting the metals at a really extreme temperature.

• Speedometers-

To know the speed of any vehicle, these currents are used. A speed indicator consists of a magnet that keeps rotating according to the speed of our vehicle. Eddy currents are been made within the drum. As the drum turns in the direction of the rotating magnet, the pointer hooked up to the drum indicates the speed of the vehicle. 

So far we've studied the electrical currents evoked in well-outlined paths in conductors like circular loops. Even when bulk pieces of conductors are subjected to ever-changing magnetic flux, induced currents are made in them. However, their flow patterns resemble whirling eddies in the water. A copper plate is allowed to swing sort of a pendulum between the pole items of a robust magnet. It’s found that the motion is damped and in a very short while the plate comes to a halt within the magnetic field. We will justify this phenomenon on the premise of electromagnetic induction. Magnetic flux related to the plate keeps on ever-changing as the plate moves in and out of the region between magnetic poles. The flux modification induces eddy currents within the plate. Directions of eddy currents are opposite once the plate swings into the region between the poles and when it swings out of the region. If rectangular slots are created within the copper plate the area available to the flow of eddy currents is a smaller amount. Thus, the pendulum plate with holes or slots reduces electromagnetic damping, and also the plate swings a lot freely. Note that magnetic moments of the induced currents (which oppose the motion) depend on the area fenced by the currents (recall equation m = ia ).

This fact is useful in reducing eddy currents within the metal like cores of transformers, electrical motors, and alternative such devices within which a coil is to be wound over metal like core. Eddy currents are undesirable since they heat up the core and dissipate electrical energy in the form of heat. Eddy currents are decreased by using laminations of metal to form a metal core. The laminations are separated by an insulating material like lacquer. The plane of the laminations should be organized parallel to the magnetic field, in order that they cut across the eddy current paths. This arrangement reduces the strength of the eddy currents. Since the dissipation of electrical energy into heat depends on the square of the strength of the electrical current, heat loss is substantially reduced.

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Previous Year Questions 

1.  If a transformer of an audio amplifier has output impedance 8000 0 and the speaker has input impedance…...[JCECE 2005]
2. A conducting loop in the shape of a right angled isosceles triangle of height 10cm10cm is kept such that the 90^∘ vertex is…..[JEE Advance 2016]
3. A 10m long horizontal wire extends from North East to South West. It is falling with a speed of 5.0ms⁻¹……. [ JEE Main 2019]
4. If a current of 2.0A2.0A flows through the smaller loop, then the flux linked with bigger loop is…… [JEE Main 2013]
5. A coil of cross-sectional area A having n turns is placed in a uniform magnetic field B….. [JEE Main 21018]
6. A copper rod of mass m slides under gravity on two smooth parallel rails, with separation ll and set at an angle of θ with the horizontal….. [JEE Main 2018]
7. A copper wire is wound on a wooden frame, whose shape is that of an equilateral…. [JEE Main 2019]
8. A metallic rod of length ll is tied to a string of length 2l and made to rotate with angular speed…. [JEE Main 2013]
9. A square frame of side 10 cm and a long straight wire carrying current 1 A are in the plane of the paper…. [JEE Main 2014]
10. If the rod makes n rotations per second, then the time averaged magnetic moment of the rod is… [JEE Main 2019]
11. Figure shows a circular area of radius R where a uniform magnetic field….
12. In a coil of resistance 100Ω , a current is induced by changing the magnetic flux through it….. [JEE Main 2017]
13. When current in a coil changes from 5A  to 2A…. [JEE Main 2015]
14. Which radiation in sunlight, causes heating effect? 
15. X -rays are….
16. Arrange the following in decreasing order of wavelength
17. Which is having minimum wavelength...[NEET 2002]
18. The speed of radio-waves is equal to….. [JIPMER 1998]
19. Gamma rays and visible light waves rays are a,ba,b and cc respectively, then….[UPSEE 2016]
20. Two identical coaxial coils P  and Q carrying equal amount of current in the same direction are brought nearer. The current in… [KEAM]

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Things to Remember

• An eddy current is a current originating in an exceeding conductor in response to a changing magnetic field.
• They flow in closed loops in an exceedingly plane perpendicular to the magnetic field.
• By Lenz law, this current swirls in such the simplest way as to produce a magnetic field opposing the change;
• For this to occur in an exceeding conductor, electrons swirl in an exceedingly plane perpendicular to the magnetic field.
• This effect was discovered in 1819-1868 by physicist Foucault and these currents are called eddy currents.
• To know the speed of any vehicle, these currents are used. A speed indicator consists of a magnet that keeps rotating according to the speed of our vehicle.
• Eddy currents are been made within the drum. As the drum turns in the direction of the rotating magnet, the pointer hooked up to the drum indicates the speed of the vehicle.