Dhristi JEE 2022-24

What is Eddy Current?

We know that whenever the magnetic flux passing through a coil changes then it will generate electromotive force and current. The same question arises when we want to know what happens when the magnetic flux is passed through a solid coil, will it also be able to induce emf and current? And the answer is yes. The current induced by the conducting body is known as the eddy current. What is eddy current is, basically eddy current is the current induced in any solid conducting body when the magnetic flux is passed through it. 


Eddy Current Definition

Eddy current is defined as the induced current in a conducting coil when a magnetic flux is allowed to flow through it or in other words, it is the induced current in a conducting body due to a change in magnetic flux. The eddy current definition can be explained as an important nature of a solid conducting body. 

Eddy Current Meaning

Now, let us have a look at the eddy current meaning and what is eddy current in detail. According to the eddy current definition we understood that it is the current generated or induced as a result of the change in magnetic flux. 


Now, what is eddy current meaning, or what do you mean by eddy current?  Whenever the conductor encounters a change in the magnetic flux, then the free electrons present in the conductor will experience a magnetic force. As a result of the effect of the magnetic force on the free electrons, these free electrons will move in the form of small loops or eddies, the electric current generated due to the motion of free electrons in the form of eddies is known as the eddy current. The generation of eddy current follows Faraday’s law of magnetic induction.


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The magnitude of induced eddy current can be calculated using Faraday’s law of magnetic induction. According to the second law of Faraday’s laws of magnetic induction, we know that induced emf is written as, rate of change of magnetic flux with respect to time will give rise to induced emf in the conductor, mathematically we get:

Emf = E = -dΦ/dt

Φ -The magnetic flux passed through the conductor

The negative sign is corresponding to the direction of the magnetic flux and is determined by the Lenz law.


Now, the current induced in a conductor whose resistance is R can be calculated by using ohm’s law, thus we get:

I= e/R

Where,

e-The emf induced in the good conductor as a result of the change in magnetic flux

R-The resistance of the conductor

Substituting the value of induced emf in the above equation we get,

I = - dΦ/dt/R = -1/RdΦ/dt

Equation (2) is known as the expression for induced current. And the direction of induced current can be estimated by the Lenz law.


Uses of Eddy Current

To understand what is eddy current it is necessary to understand Faraday’s electromagnetic induction. In rapidly changing magnetic fields, due to the production of heavy emf, large eddy currents are induced. Eddy currents are capable of producing temperature as a result of this heavy temperature. Thus a coil-over a constituent metal placed in a field of the highly oscillating magnetic field will produce a high-frequency AC. The temperature produced as a result of a heavy eddy current is enough to melt the metal. This is used to extract metals from ores.


Here are some of the uses of the eddy current:

  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 which 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


Did You Know?

The eddy current testing is nondestructive testing. And eddy current testing is an important part of our everyday life. Not everyone has heard of eddy current testing, but these methods touch all of our lives, perhaps even as a routine. This is because the eddy current techniques are used in a wide range of industries such as those industries where component failure could cause devastating damage and loss.


For an instant, the eddy current testing is used to inspect tubing and other structures for applications such as pipelines of gas and oils, nuclear reactors, chemical manufacturing, and municipal water systems. Compact and portable eddy current testing equipment is used for on-site inspections in the field, such as looking for cracks in bridges and in airplane components from wings to the landing gear. That makes ECT, and other methods of nondestructive testing, highly important to public safety playing a role in helping to prevent destructive events like pipeline breaks, bridge collapses, and plane crashes.

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FAQs (Frequently Asked Questions)

1. What is Eddy Current Induction?

The eddy current induction is the generation of current due to small current loops as a result of the change in magnetic flux.

2. Why is it termed as Eddy Current?

When the conductor encounters the change in the magnetic flux, then the free electrons present in the conductor will experience a magnetic force. As a result of the effect of the magnetic force on the free electrons, these free electrons will move in the form of small loops or eddies, the electric current generated due to the motion of free electrons in the form of eddies is known as the eddy current. 

3. What are the two main applications of Eddy Current?

The two common application areas of Eddy current are non-destructive testing (NDT) and electromagnetic damping. 


Eddy currents are used in common electromagnetic NDT methods to check materials or surfaces for cracks, discontinuities, and other faults without damaging the material or the structure itself. NDT methods are widely used in the civil engineering and construction industries. Eddy current testing uses a coil with alternating current to generate an electromagnetic field on the surface of the materials that are being studied and analyzed. 


Electromagnetic damping is a force that is generated when the eddy current is in close contact with a magnetic object or a conductor. Electromagnetic damping occurs due to a reduction in motion, which happens when an eddy current interacts with a magnetic field. So it is essentially a resistive force that causes a magnetic object to slow down, without physically touching it.


The electromagnetic damping principle is used in rail brakes. The eddy current interacts with conductive materials to slow the motion of the high-speed train without the use of physical brakes. 

4. What is Lenz’s law? 

Lenz’s law is named after the Russian physicist from the mid-nineteenth century, Emil Lenz. 


Lenz’s law states that the direction of an induced current is always such as to oppose the change in the circuit or the magnetic field that produces it.


It is a convenient method to know the direction of the induced current. The law states that the induced current flows in such a way that it converts the side of the coil nearest to the pole of the bar magnet into a north pole itself, in order to oppose the approaching bar magnet. When the bar magnet is withdrawn from the coil, the current reverses itself.


Lenz’s Law can be seen in the formula of Faraday’s law. 


The real-world applications of Lenz’s Law can be seen in Eddy current balances, metal detectors, train braking systems, AC generators, card readers, microphones, and Eddy Current dynamometers.

5. Who discovered Eddy Current?

The eddy current phenomenon was discovered in the year 1851, by French physicist Leon Foucault. For this reason, eddy currents are also referred to as Foucault currents. 


Leon Foucault built a device that placed a moving copper disk in a strong magnetic field to show that eddy currents are generated when a conducting material moves within a magnetic field.


Eddy current testing began mainly because of Michael Faraday's discovery of electromagnetic induction in 1831. He had discovered that when a magnetic field passes through a conductor or when a conductor passes through a magnetic field, an electric current will flow through the conductor if there is a closed path through which the current can circulate. Visit Vedantu to find more about Eddy current.

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