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. An electromotive force as a result of electromagnetic induction also arises if a body moves in a static and non-uniform magnetic field, or rotates in a magnetic field so that its lines intersecting a closed loop change.
Induced electric current
Under the concept of "induction" is meant the emergence of a process as a result of the impact of another process. For example, an electric current can be induced, that is, it can appear as a result of exposing a conductor to a magnetic field in a special way. Such an electric current is called induced. The conditions for the formation of an electric current as a result of the phenomenon of electromagnetic induction are discussed later in the article.
The concept of a magnetic field
BeforeTo begin studying the phenomenon of electromagnetic induction, it is necessary to understand what a magnetic field is. In simple terms, a magnetic field is a region of space in which a magnetic material exhibits its magnetic effects and properties. This region of space can be depicted using lines called magnetic field lines. The number of these lines represents a physical quantity called magnetic flux. The magnetic field lines are closed, they start at the north pole of the magnet and end at the south.
Magnetic field has the ability to act on any materials with magnetic properties, such as iron conductors of electric current. This field is characterized by magnetic induction, which is denoted B and is measured in tesla (T). A 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 coulomb, which flies perpendicular to the magnetic field lines at a speed of 1 m / s, that is, 1 T=1 Ns / (mCl).
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 a conductor through which an electric current flows createsa magnetic field around itself, that is, it begins to show magnetic properties.
Faraday, in turn, discovered the opposite of the 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 through such a circuit.
As a result, Faraday discovered a physical process, as a result of which an electric current appears in a conductor due to a change in the magnetic field, which is the phenomenon of electromagnetic induction. At the same time, for the formation of an induced current, it does not matter what moves: the magnetic field or the conductor itself. This can be easily shown by conducting an appropriate experiment on the phenomenon of electromagnetic induction. So, having placed the magnet inside the metal spiral, we begin to move it. If you connect the ends of the spiral through some indicator of electric current into a 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
Faraday's experiments consisted of working with a conductor and a permanent magnet. Michael Faraday first discovered that when a conductor moves inside a magnetic field, a potential difference arises at its ends. The moving conductor begins to cross the magnetic field lines, which simulatesthe effect of changing this field.
The scientist discovered that the positive and negative signs of the resulting potential difference depend on the direction in which the conductor moves. For example, if the conductor is raised in a magnetic field, then the resulting potential difference will have a +- polarity, but if this conductor is lowered, then we will already get a -+ polarity. These changes in the sign of the potentials, the difference of which is called the electromotive force (EMF), lead to the appearance in a closed circuit of an alternating current, 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 an induced current occurs, we will explain some of the 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 will be. Another feature of the phenomenon is as follows: the greater the magnetic induction of the field, that is, the stronger this field, the greater the potential difference it can create when moving the conductor in 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.
Electric current direction and left hand rule
To determine the direction in the conductor of an electric current created as a result of the phenomenon of electromagnetic induction, you canuse the so-called left-hand rule. It can be formulated as follows: if the left hand is placed so that the lines of magnetic induction, which begin at the north pole of the magnet, enter the palm, and the protruding thumb is directed in the direction of movement of the conductor in the field of the magnet, then the remaining four fingers of the left hand will indicate the direction of movement induced current in the conductor.
There is another version 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 the conductor, then the middle finger turned 90 degrees to the palm will indicate the direction of the appeared current in the conductor.
The phenomenon of self-induction
Hans Christian Oersted discovered the existence of a magnetic field around a conductor or coil with current. 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 resist each change in the direction of the current in the conductor or coil. This process is called self-induction. The resulting electrical differencepotentials is called the EMF of self-induction.
Note that the phenomenon of self-induction occurs not only when the direction of the current changes, but also when it changes, for example, when increasing due to a decrease in resistance in the circuit.
For the physical description of the resistance exerted by any change in current in a circuit due to self-induction, the concept of inductance was introduced, which is measured in Henry (in honor of the American physicist Joseph Henry). One henry is such an inductance for which, when the current changes by 1 ampere in 1 second, an EMF arises in the process of self-induction, equal to 1 volt.
Alternating current
When an inductor begins to rotate in a magnetic field, as a result of the phenomenon of electromagnetic induction, it creates an induced current. This electric current is variable, meaning it changes direction systematically.
Alternating current is more common than direct current. So, many devices that operate from the central electrical network use this particular type of current. Alternating current is easier to induce and transport than direct current. As a rule, the frequency of household alternating current is 50-60 Hz, that is, in 1 second its direction changes 50-60 times.
The geometric representation of 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. According to the thermal effect, alternating current is similar to currentDC, the voltage of which is Umax/√2, where Umax is the maximum voltage on the AC sinusoidal curve.
The use of electromagnetic induction in technology
The discovery of the phenomenon of electromagnetic induction produced a real boom in the development of technology. Prior to this discovery, humans were only able to produce electricity in limited quantities using electric batteries.
Currently, this physical phenomenon is used in electrical transformers, in heaters that convert induced current into heat, and in electric motors and car generators.
