[Physics Class Notes] on Eddy Current Pdf for Exam

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.

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.