Electromagnetic Induction

If the wire is then wrapped in a coil, the magnetic field is largely concentrated, creating a static magnetic field that forms the shape of a bar magnet that forms a separate North and South pole around itself.

The magnetic flux developing around the coil is proportional to the amount of current flowing in the coil windings, as shown. If additional layers of wire passing through the same coil are wrapped, the static magnetic field power increases.

Electromagnetic Induction
Air Core Empty Coil

Therefore, the magnetic field strength of a coil is determined by the amperage turns of the coil. With more wire rotations inside the coil, the greater the power of the static magnetic field around it.

But what if we reverse this idea by cutting the electric current from the coil and placing a stick magnet inside the core of the wire coil instead of a hollow core, this rod magnet will move the coil "in" and "out", inducing a current into the coil with the physical movement of the magnetic battery inside.

Similarly, if we keep the rod magnet steady and move the coil back and forth within the magnetic field, an electric current in the coil is induced. Then we can induct a voltage and current in the coil either by moving the wire or by changing the magnetic field. This process is known as Electromagnetic Induction and is the basic principle of operation of transformers, motors and generators.

Electromagnetic Induction was first discovered by Michael Faraday in the 1830s. When Faraday moved a permanent magnet in and out of a coil or a single wire ring, he noticed that it induced an electromotor force or emk, that is, a Voltage, and therefore a current was produced.

So what Michael Faraday discovered was a way to generate electric current in a circuit using only magnetic field power, not batteries. This then leads to a very important law that connects electricity with magnetism, Faraday's Electromagnetic Induction Act. So how does this work?

When the magnet shown below is moved "correctly" to the coil, the hand or needle of the Galvanometer, which is basically a very precise center zero moving coil amperemeter, will deviate only one direction from the center position. When the magnet movement stops and is held steady according to the coil, the needle of the galvanometer turns to zero, as there is no physical movement of the magnetic field.

Similarly, when the magnet is "removed" from the coil in the other direction, the needle of the galvanometer deviates in the opposite direction compared to the first, indicating a change in polarity. Then, by moving the magnet back and forth towards the coil, the needle of the galvanometer will deviate left or right, positively or negatively, according to the directional movement of the magnet.

Electromagnetic Induction with Moving Magnet

Electromagnetic Induction
Electromagnetic Induction with Moving Magnet

Similarly, if the magnet is kept steady now and moved only towards or away from the coil magnet, the needle of the galvanometer will deviate in both directions. Next, the action of moving a coil or wire ring within a magnetic field induces a voltage in the coil, and the magnitude of this induced voltage is proportional to the speed or speed of movement.

Then we can see that the faster the movement of the magnetic field, the larger the induced impregnation or voltage in the coil, so for the Faraday law to be correct, there must be "relative movement" or movement between the coil and the magnetic field.

Faraday's Induction Act

From the above statement, we can say that there is a relationship between an electric voltage and a changing magnetic field, as stated by Michael Faraday's famous electromagnetic induction law: "When there is relative movement between a conductor and a magnetic, a voltage is induced in one circuit. the area and the magnitude of this voltage are proportional to the rate of change of the influx." In other words, electromagnetic induction is the process of using magnetic fields to generate voltage and current in a closed circuit.

So just how much voltage (emk) can be induced into the coil using magnetism. This is determined by the following 3 different factors.

  • Increasing the number of wire wraps in the coil – increasing the amount of individual conductors that cut the magnetic field, the amount of induced emk produced will be the sum of all individual cycles of the coil, So if there are 20 turns, the coil will be 20 times more induced sucking than one piece of wire.
  • Increasing the speed of relative movement between the coil and the magnet – if the same wire coil passes through the same magnetic field and its speed increases, the wire will cut the flux lines faster, thereby inducing more emk..
  • Increasing the power of the magnetic field – If the same wire coil is moved at the same speed within a stronger magnetic field, more emk will be produced as there are more force lines to be cut.

If we could move the magnet in the diagram above at a constant speed and distance without stopping inside and outside the coil, it would produce a continuously induced voltage ranging from a positive pole to a negative pole and produce alternative or AC output. voltage and this is the basic principle of the operation of an electric generator in a similar way to those used in dynamo and car alternators.

In small generators, such as bicycle dynamo, a small permanent magnet is rotated by the movement of the bicycle wheel in a stationary coil. Alternatively, in both cases, an electromagnet powered by a constant DC voltage can be rotated in a fixed coil, as in large power generators that produce an alternating current.

Simple Generator Using Magnetic Induction

Electromagnetic Induction
Simple Generator Using Magnetic Induction

The simple dynamo type generator above consists of a permanent magnet that rotates around a central shaft with a wire coil placed next to this rotating magnetic field. As the magnet rotates, the magnetic field at the top and bottom of the coil constantly varies between the north and south pole. This rotational motion of the magnetic field results in an alternate impetus induced in the coil, as defined by Faraday's electromagnetic induction law.

The magnitude of the electromagnetic induction is directly proportional to the flux density, β is given by the expression of motion emk, the total length of the conductor, the speed or speed at which the magnetic field in the conductor varies in meters per meter and the magnetic field in the conductor in meters/second, the number of cycles emitting or m/s:

Faraday's Moving EMK Statement

Electromagnetic Induction

If the conductor does not move at right angles to the magnetic field (90°), a reduced output is obtained as the angle increases by adding an angle of ε° to the above expression:

Lenz's Electromagnetic Induction Act

Faraday's Law tells us that voltage induction to a conductor can be done by passing it through a magnetic field or by passing the magnetic field through the conductor, and if this conductor is part of a closed circuit, an electric current will flow. This voltage is called an induced emk, since it is induced into the conductor by a magnetic field that changes due to electromagnetic induction, which tells us the direction (or polarity of the induced emk) with the negative signal in faraday law.

But a changing magnetic flux produces a changing current along the coil, which will produce its own magnetic field, as we have seen in the training of electromagnets. This self-induced emk opposes the change that causes it, and the faster the rate of change of the current, the greater the opposing emk. This self-induced emk will oppose the change in the current in the coil according to Lenz law. Due to its direction, this self-induced emk is often called back emk.

The Lenz Act says: "the direction of a stimulated emk is always to oppose the change that causes it." In other words, an induced current is always opposed to the movement or change that initiates the induced current at first, and this idea is found in inductainment analysis. Similarly, if the magnetic flux decreases, then the induced emk will oppose this reduction by producing and inducing magnetic flux added to the original flux.

The Lenz law is one of the basic laws in electromagnetic induction to determine the direction of flow of induced currents and relates to the law of energy conservation. According to the law on the protection of energy, which specifies that the total amount of energy in the universe will always remain constant, energy cannot be created or destroyed. The Lenz law is derived from Michael Faraday's induction law.

One last comment on the Lenz Act on electromagnetic induction. Now we know that when there is a relative movement between a conductor and a magnetic field, an emk is induced within the conductor.

However, the conductor may not actually be part of the electrical circuitry of the coils, but it can be the iron core of the coils or another metallic part of the system, such as a transformer. The emk induced in this metallic part of the system causes a current to flow around it, and this type of core current is known as the Vortex Current (Eddy current).

Vortex currents produced by electromagnetic induction circulate around the coil core or any metallic component within the magnetic field, as they act like a single wire loop for magnetic flux. Vortex currents do not contribute to the usefulness of the system. Instead, they oppose the flow of induced current by acting as a negative force that produces resistant heating and power loss within the core. However, there are applications for electromagnetic induction furnaces where only vortex currents are used to heat and melt ferromagetic metals.

Vortex Currents Circulating in a Transformer

Electromagnetic Induction
Vortex Currents Circulating in a Transformer

The changing magnetic flux in the iron core of a transformer above will induct an emk not only in the primary and secondary windings, but also in the iron core. The iron core is a good conductor, so the currents induced in a solid iron core will be large. In addition, vortex currents flow in a direction that acts in a way that weakens the flux generated by the primary coil, according to the Lenz law. As a result, the current in the primary coil required to produce a specific area B increases, so the hysteresis curves are thicker along the H-axis.

Electromagnetic Induction

Vortex current and hysteresis losses cannot be completely eliminated but can be greatly reduced. Instead of having a solid iron core as the magnetic core material of the transformer or coil, the magnetic path is "laminated".

These laminations are very finely insulated (usually varnished) metal strips that are combined to produce a solid core. Laminations increase the resistance of the iron core, thereby increasing the overall resistance to the flow of vortex currents, thereby reducing the power loss of the induced vortex current in the core, and therefore the magnetic iron circuit of transformers and all electrical machines are laminated.