An Introduction to Eddy Current
Prior to obtaining a clear scenario on Eddy now, let us begin to know its set of experiences, how it was created, and what are its improvements.
The initial researcher to investigate the idea of Eddy Current was Arago in the year 1786 - 1853. Though in the time frame between 1819 – 1868, Foucault acquired credits in the disclosure of Eddy Current.
Furthermore, the principal use of Eddy Current happens for a non-damaging investigation that occurred in the year 1879 when Hughes carried out the ideas of leading metallurgical ordering tests.
Presently, this page gives a reasonable clarification of the eddy current generator, eddy current principle, and the use of eddy current.
Eddy Current Principle
An eddy current is also called the Foucault current. Eddy currents are swirls of electric currents induced within conductors by a changing magnetic field within the conductor (self-inductance). Eddy current works on the principle of Faraday’s law of induction.
The Eddy Current Principle works as the Self-inductance.
One must note that Eddy currents can be induced within nearby static conductors by a time-varying magnetic field created by an AC electromagnet or transformer. For instance, by relative motion between a magnet and a conductor (Eddy Current Aluminium).
On this page, you will learn about the Eddy current and the use of Eddy current in detail.
Eddy Current Flow
Eddy current flows in a closed loop within the conductors only and always acts in a plane perpendicular to the magnetic field.
The magnitude of the current in a given circle is relative to the strength of the magnetic field, the area of the circle, the pace of magnetic flux, and conversely corresponding to the resistivity of the material.
At the point when charted/graphed, these roundabout flows inside a piece of metal look enigmatically like Eddies or whirlpools in a fluid.
Eddy Current Magnetic Field
Eddy currents are likewise called Foucault's currents and flow where these streams around the conductors pivot in whirls in streams. These are simulated by fluctuating the magnetic fields and development in closed rings, which are in a vertical situation to the magnetic field's plane (Eddy Current Magnet).
Eddy current flow can be created when there is a conductor movement across the magnetic field or when there is variety in the magnetic field that encases the fixed channel.
This implies that anything that results in the conductor faces a changeover either in the direction of the magnetic field or intensity and this conveys these circling current flows. The magnitude of this current has the direct extent to the magnetic field magnitude, circle cross-sectional region, and measure of flux in the transition and has a converse relative rate to the conductor's resistivity. This is the fundamental Eddy Current Principle.
By Lenz's law, a swirling or an Eddy current makes a magnetic field that goes against the change in the magnetic field that made it, and accordingly, Eddy Current (whirlpool flows) reacts back on the source of the magnetic field.
For instance, a close-by conductive surface will apply a drag power on a moving magnet that goes against its movement, because of eddy current induced in the surface by the moving magnetic field.
Use of Eddy Current
This impact is utilized in Eddy current brakes which are utilized to quit pivoting power apparatuses immediately when they are stopped. The current coursing through the opposition of the conductor additionally scatters energy as warmth in the material.
Eddy Current Generator
A magnet actuates roundabout electric flows in a metal sheet travelling through its attractive field. See the graph at right. It shows a metal sheet (C) moving to one side under a fixed magnet. The attractive field (B, green bolts) of the magnet's north pole N goes down through the sheet.
Eddy Current Aluminium
Since the metal (aluminum/copper) is moving, the flux through a given territory of the sheet is evolving. In the piece of the sheet moving under the main edge of the magnet (left-side) the magnetic field through a given point on the sheet is expanding as it gets closer to the magnet, {dB/dt > 0}.
From Faraday's law of enlistment, this makes a looping electric field in the sheet a counterclockwise way around the magnetic field lines. This field initiates a counterclockwise progression of electric flow (I, red), in the sheet. This is the Eddy current.
Use of Eddy Current
Eddy currents are used to heat objects in induction heating furnaces and equipment, and to distinguish breaks and defects in metal parts utilizing Eddy current testing instruments.
Eddy Current Separator
An Eddy current separator utilizes an incredibly magnetic field to isolate non-ferrous metals from wastage after all ferrous metals have been taken out already by some previous arrangement of magnets.
The device utilizes Eddy’s current flow to impact the separation. The Eddy current separator is not intended to sort ferrous metals which become hot inside the swirl current field, as this can prompt harm to the separator unit belt.
Benefits of Eddy Current
This method is particularly effective in the analysis process
This is a non-impact analysis process that does not show an impact on the work
The analysis is completely fast and gives accurate results
The cover is easily analyzed which is used in many products
It is even used on a speedometer device and in the process of an indoor furnace.
Disadvantages of Eddy Current
As a result of this process, there will be a leak of magnetic flux
Severe heat loss occurs due to cyclic currents due to the collision of the magnetic circuit. With this electric current, it wastes as a form of heat
Eddy Current Applications
It is done on trains with eddy current brakes
It is used to provide decent torque to PMMC devices
It is used in electrical devices as an input power meter
These are used to determine the damage to the metal sections
Eddy Currents Properties
These are made only within the operating equipment.
These are distorted by faults such as cracks, rust, edges, etc.
Eddy currents diminish in-depth with the larger forces present above.
These structures lead to the widespread use of eddy currents in energy, aerospace, and petrochemical industries to detect cracking and metal damage.
Causes of Eddy Currents
When the conductor moves in a magnetic field or when the magnetic field surrounding a vertical conductor changes, eddy currents are produced. Eddy currents can therefore be made whenever the strength or direction of the magnetic field changes in the conductor.
We know from Lenz Law that the direction of induced current, like eddy current, will be such that the magnetic field created by it opposes the changes in the magnetic field that it caused. The electrons in the conductor rotate in a plane that relies on a magnetic field for this to happen. The size of the eddy current is:
Depending on the size of the magnetic field
Equivalent to the loop area
In proportion to the degree of fluctuations of the magnetic fluctuations in reverse
In line with the resistance of the conductor
Eddy currents often fight off changes in the magnetic field they produce, resulting in a loss of power to the conductor. These convert heat into heat, such as kinetic or electrical energy. In order to stabilize rotating power tools and rollercoasters, we use resistance caused by opposing backgrounds to produce eddy currents.
FAQs on Eddy Current
1. What are eddy currents as per the Class 12 Physics syllabus?
Eddy currents, also known as Foucault currents, are loops of electric current induced within conductors by a changing magnetic field in the conductor, according to Faraday's law of induction. These currents flow in closed loops within the conductor, in planes perpendicular to the magnetic field. They are named 'eddy' currents because they resemble the swirling eddies seen in a fluid.
2. What is the fundamental principle that governs the formation and direction of eddy currents?
The formation of eddy currents is governed by two fundamental principles of electromagnetism:
- Faraday's Law of Induction: This law states that any change in the magnetic environment of a conductor will cause a voltage (EMF) to be 'induced' in the conductor. This induced EMF drives the flow of current.
- Lenz's Law: This law determines the direction of the induced eddy currents. It states that the direction of the current will be such that it creates a magnetic field that opposes the change in the magnetic flux that produced it. This opposition is the reason for effects like magnetic braking.
3. What are some important practical applications of eddy currents?
While often seen as a source of energy loss, eddy currents have several useful applications. Key examples include:
- Magnetic Braking: Used in high-speed trains and roller coasters, where strong electromagnets induce eddy currents in the metal rails or fins. The opposing magnetic field created by the eddy currents provides a smooth, non-contact braking force.
- Induction Furnaces: High-frequency changing magnetic fields induce large eddy currents in a metal piece, generating immense heat (due to I²R loss) to melt the metal.
- Electromagnetic Damping: In devices like galvanometers, eddy currents are induced in the soft iron core to bring the moving coil to rest quickly, preventing unwanted oscillations.
- Induction Cooktops: A changing magnetic field from a coil beneath the ceramic surface induces eddy currents directly in the metallic cookware, which then heats up and cooks the food.
4. Why are eddy currents considered a problem in devices like transformers?
In devices like transformers and electric motors, the primary goal is to efficiently transfer energy via magnetic fields. However, the changing magnetic flux in the iron core also induces strong eddy currents. These currents circulate within the core, and as they flow through the resistive material of the core, they dissipate energy in the form of unwanted heat (Joule heating). This represents a significant power loss, reduces the efficiency of the device, and can lead to overheating and damage.
5. How are eddy currents minimised in a transformer's core?
To minimise energy loss from eddy currents in a transformer, the solid iron core is replaced with a laminated core. This means the core is constructed from thin sheets of iron, each electrically insulated from the next by a thin layer of varnish or oxide. This design forces the eddy currents to flow in much smaller, less intense loops within each lamination, dramatically increasing the overall resistance to their path and thus significantly reducing the energy lost as heat.
6. How do eddy current brakes differ from traditional friction-based brakes?
Eddy current brakes and friction brakes operate on entirely different principles and offer different advantages:
- Mechanism: Friction brakes work by pressing a pad against a disc or drum, converting kinetic energy into heat through friction. Eddy current brakes are non-contact; they use magnetic fields to induce currents that create an opposing magnetic force, converting kinetic energy into heat within the conductor itself.
- Wear and Tear: Since they are non-contact, eddy current brakes experience virtually no mechanical wear, leading to longer life and lower maintenance. Friction brakes wear down over time and require regular replacement.
- Performance: The braking force from eddy currents is proportional to the speed, meaning it is strongest at high speeds and diminishes as the object slows down, resulting in very smooth deceleration. Friction brakes can be more abrupt.
7. Can eddy currents be induced in non-magnetic metals like aluminium or copper?
Yes, absolutely. The induction of eddy currents primarily depends on the material being an electrical conductor, not on whether it is magnetic. A changing magnetic field will induce eddy currents in any conductor, including aluminium, copper, and gold. In fact, aluminium and copper are excellent for demonstrating eddy current effects (like in magnetic braking fins) because they have very low electrical resistance, allowing significant currents to flow.
