The phenomenon of electromagnetic induction is a phenomenon that consists in the occurrence of an electromotive force or voltage in a body located in a magnetic field that is constantly changing. Electromotive force as a result of electromagnetic induction also occurs if the body moves in a static and inhomogeneous magnetic field or rotates in a magnetic field so that its lines crossing a closed circuit change.
Induced electric current
The term "induction" means the emergence of a process as a result of the influence of another process. For example, an electric current can be induced, that is, it can appear as a result of a special effect on a magnetic field conductor. Such an electric current is called induced. The conditions for the formation of electric current as a result of the phenomenon of electromagnetic induction are considered further in the article.
The concept of magnetic field
Before you begin to study the phenomenon of electromagnetic induction, you need to understand what constitutes a magnetic field. In simple words, by a magnetic field is meant a region of space in which a magnetic material exhibits its magnetic effects and properties. This region of space can be represented using lines called magnetic field lines. The quantity of these lines represents a physical quantity called magnetic flux. The magnetic field lines are closed, they begin at the north pole of the magnet and end at the south.
A magnetic field has the ability to act on any materials with magnetic properties, for example, iron conductors of electric current. This field is characterized by magnetic induction, which is denoted by B and is measured in tesla (T). Magnetic induction of 1 T is a very strong magnetic field that acts with a force of 1 Newton on a point charge of 1 pendant, which flies perpendicular to the lines of the magnetic field at a speed of 1 m / s, i.e. 1 T = 1 N * s / ( m * C).
Who discovered the phenomenon of electromagnetic induction?
Electromagnetic induction, on the principle of which many modern devices are based, was discovered in the early 30s of the XIX century. The discovery of the phenomenon of electromagnetic induction is usually attributed to Michael Faraday (discovery date - August 29, 1831). The scientist was based on the results of the experiments of the Danish physicist and chemist Hans Oersted, who discovered that the conductor through which electric current flows creates a magnetic field around itself, that is, it begins to exhibit magnetic properties.
Faraday, in turn, discovered the opposite phenomenon discovered by Oersted. He noticed that a changing magnetic field, which can be created by changing the parameters of the electric current in the conductor, leads to the appearance of a potential difference at the ends of any current conductor. If these ends are connected, for example, through an electric lamp, then an electric current will flow along such a circuit.
As a result, Faraday discovered a physical process, as a result of which an electric current appears in the conductor due to a change in the magnetic field, which is the phenomenon of electromagnetic induction. Moreover, for the formation of the induced current, it does not matter what moves: the magnetic field or the conductor itself . This can easily be shown by conducting an appropriate experiment on the phenomenon of electromagnetic induction. So, placing a magnet inside a metal spiral, we begin to move it. If you connect the ends of the spiral through any indicator of electric current in the circuit, you can see the appearance of current. Now you should leave the magnet alone and move the spiral up and down relative to the magnet. The indicator will also show the existence of current in the circuit.
Faraday experiment
The experiments of Faraday consisted in working with a conductor and a permanent magnet. For the first time, Michael Faraday discovered that when a conductor moves inside a magnetic field, a potential difference arises at its ends. A moving conductor begins to cross the lines of the magnetic field, which simulates the effect of a change in this field.
The scientist found that the positive and negative signs of the resulting potential difference depend on in which direction the conductor moves. For example, if the conductor is raised in a magnetic field, then the resulting potential difference will have a polarity of + -, if you lower this conductor, then we will already get the polarity of - +. These changes in the sign of potentials, the difference of which is called electromotive force (EMF), lead to the appearance of an alternating current in a closed circuit, that is, a current that constantly changes its direction to the opposite.
Features of electromagnetic induction discovered by Faraday
Knowing who discovered the phenomenon of electromagnetic induction and why the induced current occurs, we explain some features of this phenomenon. So, the faster you move the conductor in a magnetic field, the greater the value of the induced current in the circuit. Another feature of the phenomenon is the following: the greater the magnetic induction of the field, that is, the stronger this field, the greater the potential difference it can create when the conductor moves into the field. If the conductor is at rest in a magnetic field, no EMF arises in it, since there is no change in the lines of magnetic induction crossing the conductor.
Direction of electric current and rule of the left hand
To determine the direction in the conductor of an electric current created as a result of the phenomenon of electromagnetic induction, you can use the so-called left-hand rule. It can be formulated as follows: if the left hand is positioned so that the lines of magnetic induction that begin at the north pole of the magnet enter the palm of the hand, and the protruding thumb is directed in the direction of movement of the conductor in the magnet field, then the remaining four fingers of the left hand will indicate the direction of movement induced current in the conductor.
There is another variant of this rule, it is as follows: if the index finger of the left hand is directed along the lines of magnetic induction, and the protruding thumb is directed in the direction of movement of the conductor, then the middle finger turned 90 degrees to the palm will indicate the direction of the current that has appeared in the conductor.
The phenomenon of self-induction
Hans Christian Oersted discovered the existence of a magnetic field around a conductor or current coil. The scientist also found that the characteristics of this field are directly related to the strength of the current and its direction. If the current in the coil or conductor is variable, then it will generate a magnetic field that will not be stationary, that is, it will change. In turn, this alternating field will lead to the appearance of an induced current (the phenomenon of electromagnetic induction). The movement of the induction current will always be opposite to the alternating current circulating through the conductor, that is, it will provide resistance with every change in the direction of the current in the conductor or coil. This process is called self-induction. The resulting electric potential difference is called the self-induction EMF.
Note that the phenomenon of self-induction occurs not only when the current direction changes, but also when it changes in any way, for example, when it increases due to a decrease in the resistance in the circuit.
The concept of inductance, which is measured in Henry (in honor of the American physicist Joseph Henry), was introduced for a physical description of the resistance exerted by any change in the current in the circuit due to self-induction. One henry is such an inductance for which, when the current changes for 1 second by 1 ampere, an EMF of 1 volt occurs during self-induction.
Alternating current
When the inductor begins to rotate in a magnetic field, then as a result of the phenomenon of electromagnetic induction, it creates an induced current. This electric current is variable, that is, it systematically changes its direction.
Alternating current is more common than direct current. So, many devices that operate from a central electrical network use this type of current. Alternating current is easier to induce and transport than direct. As a rule, the frequency of household alternating current is 50-60 Hz, that is, in 1 second its direction changes 50-60 times.
A geometric image of an alternating current is a sinusoidal curve that describes the dependence of voltage on time. The full period of the sinusoidal curve for household current is approximately 20 milliseconds. In terms of thermal effect, alternating current is similar to direct current, whose voltage is U max / √2, where U max is the maximum voltage on the sinusoidal curve of alternating current.
The use of electromagnetic induction in technology
The discovery of the phenomenon of electromagnetic induction made a real boom in the development of technology. Prior to this discovery, people were only able to produce electricity in limited quantities with the help of electric batteries.
Currently, this physical phenomenon is used in electric transformers, in heaters that convert induced current to heat, and also in electric motors and car generators.