One of the most important branches of modern physics is this and all the definitions associated with it. It is this interaction that explains all electrical phenomena. The theory of electricity covers many other areas, including optics, since light is electromagnetic radiation. In this article we will try to explain the essence of electric current and magnetic force in an accessible, understandable language.
Magnetism - the foundation of the foundations
In childhood, adults showed us various magic tricks using magnets. These amazing figurines, which are attracted to each other and can attract small toys, have always pleased the children's eyes. What are magnets and how does the magnetic force act on iron parts?
Explaining in a scientific language, you will have to turn to one of the basic laws of physics. According to Coulomb's law and the special theory of relativity, a certain force acts on the charge, which is directly proportional to the speed of the charge itself (v). It is this interaction that is called the magnetic force.
Physical Features
In general, it should be understood that any arise only when charges move inside the conductor or in the presence of currents in them. When studying magnets and the very definition of magnetism, it should be understood that they are closely related to the phenomenon of electric current. Therefore, let's understand the essence of electric current.
The electrical force is the force that acts between an electron and a proton. It is numerically much greater than the value of the gravitational force. It is generated by an electric charge, or rather, by its movement inside the conductor. Charges, in turn, are of two types: positive and negative. As you know, positively charged particles are attracted to negatively charged ones. However, charges of the same sign tend to repel each other.
So, when these same charges begin to move in the conductor, an electric current arises in it, which is explained as the ratio of the amount of charge flowing through the conductor in 1 second. The force acting on a conductor with current in a magnetic field is called the Ampere force and is found according to the "left hand" rule.
Empirical data
You can encounter magnetic interaction in everyday life when dealing with permanent magnets, inductors, relays or electric motors. Each of them has a magnetic field that is invisible to the eye. It can be traced only by its effect, which it has on moving particles and on magnetized bodies.
The force acting on a current-carrying conductor in a magnetic field was studied and described by the French physicist Ampère. Not only this force is named after him, but also the magnitude of the current strength. At school, Ampère's laws are defined as the rules of "left" and "right" hand.
Magnetic field characteristics
It should be understood that a magnetic field always arises not only around sources of electric current, but also around magnets. He is usually depicted with magnetic lines of force. Graphically, it looks as if a sheet of paper was placed on a magnet, and iron filings were poured on top. They will look exactly like the picture below.
In many popular books on physics, the magnetic force is introduced as a result of experimental observations. It is considered a separate fundamental force of nature. Such an idea is erroneous; in fact, the existence of a magnetic force follows from the principle of relativity. Its absence would lead to violation of this principle.
There is nothing fundamental about the magnetic force - it is simply a relativistic consequence of Coulomb's law.
Application of magnets
According to the legend, in the first century AD, on the island of Magnesia, the ancient Greeks discovered unusual stones that had amazing properties. They attracted to themselves any thing made of iron or steel. The Greeks began to take them out of the island and study their properties. And when the stones fell into the hands of street magicians, they became indispensable helpers in all their performances. Using the power of magnetic stones, they managed to create a whole fantastic show that attracted many viewers.
As the stones spread to all parts of the world, legends and various myths began to circulate about them. Once the stones ended up in China, where they were named after the island on which they were found. Magnets became the subject of study of all the great scientists of that time. It has been noticed that if you put a magnetic ironstone on a wooden float, fix it, and then turn it, it will try to return to its original position. Simply put, the magnetic force acting on it will turn the iron ore in a certain way.
Using this, scientists came up with a compass. On a round shape made of wood or cork, two main poles were drawn and a small magnetic needle was installed. This design was lowered into a small bowl filled with water. Over time, compass models have improved and become more accurate. They are used not only by sailors, but also by ordinary tourists who like to explore desert and mountainous areas.
The scientist Hans Oersted devoted almost his entire life to electricity and magnets. One day, during a lecture at the university, he showed his students the following experience. He passed a current through an ordinary copper conductor, after a while the conductor heated up and began to bend. This was a phenomenon of the thermal property of the electric current. The students continued these experiments, and one of them noticed that the electric current has another interesting property. When a current flowed in the conductor, the arrow of the compass located nearby began to deviate little by little. Studying this phenomenon in more detail, the scientist discovered the so-called force acting on a conductor in a magnetic field.
Ampere currents in magnets
Scientists have attempted to find a magnetic charge, but an isolated magnetic pole could not be found. This is explained by the fact that, unlike electric, magnetic charges do not exist. After all, otherwise it would be possible to separate a unit charge by simply breaking off one of the ends of the magnet. However, a new opposite pole is formed at the other end.
In fact, any magnet is a solenoid, on the surface of which intra-atomic currents circulate, they are called Ampère currents. It turns out that the magnet can be considered as a metal rod through which a direct current circulates. It is for this reason that the introduction of an iron core into the solenoid significantly increases the magnetic field.
Magnet energy or EMF
Like any physical phenomenon, a magnetic field has energy that it spends on moving a charge. There is the concept of EMF (electromotive force), it is defined as the work of moving a unit charge from point A 0 to point A 1.
EMF is described by Faraday's laws, which are applied in three different physical situations:
- Conducted circuit moves in the generated uniform magnetic field. In this case, we speak of magnetic emf.
- The circuit is at rest, but the source of the magnetic field itself is moving. This is the phenomenon of electric emf.
- And finally, the circuit and the source of the magnetic field are stationary, but the current that creates the magnetic field changes.
Numerically, the EMF according to the Faraday formula is: EMF \u003d W / q.
Therefore, the electromotive force is not a force in the literal sense, since it is measured in Joules per Coulomb or in Volts. It turns out that it represents the energy that is imparted to the conduction electron when bypassing the circuit. Each time, making the next round of the rotating frame of the generator, the electron acquires an energy numerically equal to the EMF. This additional energy can not only be transferred during collisions of atoms in the outer chain, but also released in the form of Joule heat.
Lorentz force and magnets
The force acting on the current in a magnetic field is determined by the following formula: q*|v|*|B|*sin a (the product of the magnetic field charge, the velocity modules of the same particle, the field induction vector and the sine of the angle between their directions). The force that acts on a moving unit charge in a magnetic field is called the Lorentz force. An interesting fact is that Newton's 3rd law is invalid for this force. It obeys only that is why all the tasks of finding the Lorentz force should be solved on the basis of it. Let's see how you can determine the strength of the magnetic field.
Tasks and examples of solutions
To find the force that arises around a conductor with current, it is necessary to know several quantities: the charge, its speed and the value of the induction of the resulting magnetic field. The following problem will help you understand how to calculate the Lorentz force.
Determine the force acting on a proton that moves at a speed of 10 mm / s in a magnetic field with an induction of 0.2 C (the angle between them is 90 o, since the charged particle moves perpendicular to the lines of induction). The solution comes down to finding the charge. Looking at the table of charges, we find that the proton has a charge of 1.6 * 10 -19 C. Next, we calculate the force according to the formula: 1.6 * 10 -19 * 10 * 0.2 * 1 (the sine of the right angle is 1) = 3.2 * 10 -19 Newtons.
Knowledge of what the Ampere force is, how it relates and how it can be useful to people is necessary for those who work with current. Both for your own safety and for working with various radio electronics (when designing railguns, which is quite popular). But enough walking around, let's get down to finding out what the Ampere force is, the features of this force and where it is used. It will also be possible to read the potential for future use and the benefits of using it now.
Ampère's law
Ampère's force is the main component of Ampère's law - the law of the interaction of electric currents. It states that in parallel conductors in which electric currents flow in the same direction, an attractive force arises. And in those conductors in which electric currents flow in opposite directions, a repulsive force arises.
Ampère's law is also called the law that determines the strength of the magnetic field on a small part of the conductor through which the current flows. In this case, it is defined as the result of multiplying the current density that flows through the conductor by the induction of the magnetic field in which the conductor is located.
From the Ampere law itself, it was concluded that the Ampère force is zero if the angle located between the current and the magnetic induction line is also zero. In other words, the conductor to achieve zero value must be located along the line of magnetic induction.
And what is the power of Ampere?
This is the force with which the magnetic field affects the part of the conductor through which the current flows. The conductor itself is in a magnetic field. The Ampere force directly depends on the strength of the current in the conductor and the vector product of the length of the part of the conductor, multiplied by the magnetic induction.
In formula form, it will look like this: sa \u003d st * dchp * mi. Here:
- sa - Ampere's power,
- st - current strength,
- dchp - the length of the conductor part,
- mi - magnetic induction.
Discovery history
It was first formulated by André Ampère, who applied the law to direct current. It was opened in 1820. This law had far-reaching consequences in the future, because without it it is simply impossible to imagine the operation of a number of electrical devices.
left hand rule
This rule helps to remember the direction of Ampere's force. The rule itself sounds like this: if the hand occupies such a position that the lines of the magnetic induction of the external field go into the palm, and the fingers from the little finger to the index finger indicate the direction in the direction of the current in the conductor, then the thumb of the palm of the hand, rejected at an angle of 90 degrees, will indicate , where the Ampere force acting on the conductor element is directed. There may be some difficulty in using this rule, but only if the angle between the current and the field induction is too small. For ease of application of this rule, the palm is often positioned so that it does not include a vector, but a magnetic induction modulus (as shown in the picture).
Ampere Force (when using two parallel conductors)
Imagine two infinite conductors that are located at a certain distance. Current flows through them. If currents flow in the same direction, then the conductors attract. Otherwise, they will repel one from one. The fields that create parallel conductors are directed opposite to each other. And to understand why they react in this way, you just need to remember that like poles of magnets or like charges always repel each other. To determine the side of the direction of the field created by the conductor, you should use the rule of the right screw.
Application of knowledge about the power of Ampere
You can meet the field of application of knowledge about the power of Ampere at almost every step of civilization. The use of Ampere's force is so extensive that it is even difficult for an average citizen to imagine what can be done, knowing Ampere's law and the features of the use of force. So, under the action of the Ampere force, the rotor rotates, the winding of which is influenced by the magnetic field of the stator, and the rotor starts to move. Any vehicle that uses electric propulsion to turn the shafts (which connect the wheels of a vehicle) uses an ampere force (this can be seen on trams, electric locomotives, electric cars, and many other interesting modes of transport). Also, it is the magnetic field that affects the mechanisms, which are electrical devices that must open / close something (elevator doors, opening gates, electric doors and many others). In other words, all devices that cannot work without electricity and have movable nodes work thanks to knowledge of Ampère's law. For example:
- Any components in electrical engineering. The most popular is the elementary electric motor.
- Various types of electrical engineering that generates various sound vibrations using a permanent magnet. The mechanism of action is such that an electromagnetic field acts on the magnet, which creates a current-carrying conductor located nearby, and a change in voltage leads to a change in the sound frequency.
- The work of electromechanical machines is built on the Ampere force, in which the movement of the rotor winding occurs relative to the stator winding.
- With the help of the Ampère force, an electrodynamic process of plasma compression takes place, which has found application in tokamaks and potentially opens up vast ways for the development of thermonuclear energy.
- Also, with the help of electrodynamic compression, an electrodynamic pressing method is used.
Potential
Despite the already existing practical application, the potential for using the Ampère force is so huge that it is difficult to describe. It can be used in complex mechanisms that are designed to facilitate the existence of a person, automate his activities, and also improve natural life processes.
Experiment
In order to be able to see with your own eyes the effect of Ampere's force, you can conduct a small experiment at home. First you need to take a horseshoe magnet, in which a conductor is placed between the poles. Everything is desirable to reproduce as in the picture. If you close the key, you can see that the conductor will begin to move, shifting from the starting point of equilibrium. You can experiment with the directions of current flow and see that depending on the direction of movement, the direction of deflection of the conductor changes. From the experiment itself, several observations can be made that confirm the above:
- The magnetic field acts exclusively on a current-carrying conductor.
- A current-carrying conductor in a magnetic field is subjected to a force that is a consequence of their interaction. It is under the influence of this force that the conductor moves in space within the boundaries of the magnetic field.
- The nature of the interaction directly depends on the voltage of the electric current and the magnetic field lines.
- The field does not act on a current-carrying conductor if the current in the conductor flows parallel to the direction of the field lines.
Safety when working with current
When working with electric current, you must follow a few simple safety rules that will allow you to avoid negative consequences:
- Work with power sources not exceeding 12 volts.
- Do not work on flammable materials.
- Do not work with wet hands.
- Do not touch live parts of the device.
The French physicist Dominique Francois Arago (1786-1853) at a meeting of the Paris Academy of Sciences spoke about Oersted's experiments and repeated them. Arago proposed a natural, as it seemed to everyone, explanation of the magnetic action of electric current: the conductor, as a result of the flow of electric current through it, turns into a magnet. Another academician, mathematician André Marie Ampère, attended the demonstration. He suggested that the essence of the newly discovered phenomenon is in the movement of the charge, and decided to take the necessary measurements himself. Ampère was sure that closed currents were equivalent to magnets. On September 24, 1820, he connected two wire spirals to a voltaic column, which turned into magnets.
That. a coil with current creates the same field as a bar magnet. Ampere created the prototype of the electromagnet, discovering that a steel bar placed inside a current-carrying spiral becomes magnetized, amplifying the magnetic field many times over. Ampere suggested that the magnet is a certain system of internal closed currents and showed (both on the basis of experiments and with the help of calculations) that a small circular current (coil) is equivalent to a small magnet located in the center of the coil perpendicular to its plane, i.e. any circuit with current can be replaced by a magnet of infinitely small thickness.
Ampere's hypothesis that inside any magnet there are closed currents, called. hypothesis of molecular currents and formed the basis of the theory of interaction of currents - electrodynamics.
A current-carrying conductor in a magnetic field is subject to a force that is determined only by the properties of the field at the location where the conductor is located, and does not depend on which system of currents or permanent magnets created the field. The magnetic field has an orienting effect on the frame with current. Consequently, the torque experienced by the frame is the result of the action of forces on its individual elements.
Ampère's law can be used to determine the modulus of the magnetic induction vector. The modulus of the induction vector at a given point of a uniform magnetic field is equal to the greatest force that acts on a conductor of unit length placed in the vicinity of a given point, through which a current flows per unit of current strength: . The value is achieved provided that the conductor is perpendicular to the lines of induction.
Ampère's law is used to determine the strength of the interaction of two currents.
Between two parallel infinitely long conductors, through which direct currents flow, an interaction force arises. Conductors with the same direction of currents attract, those with oppositely directed currents repel.
The power of interaction per unit length of each of the parallel conductors is proportional to the magnitude of the currents and and inversely proportional to the distance between R between them. This interaction of conductors with parallel currents is explained by the left hand rule. The modulus of force acting on two infinite rectilinear currents and , the distance between which is equal to R.
The ampere force is the force with which a magnetic field acts on a current-carrying conductor placed in this field. The magnitude of this force can be determined using Ampère's law. This law defines an infinitely small force for an infinitely small section of the conductor. This makes it possible to apply this law to conductors of various shapes.
Formula 1 - Ampère's Law
B the induction of the magnetic field in which the current-carrying conductor is located
I current in a conductor
dl an infinitesimal element of the length of a current-carrying conductor
alpha angle between the induction of an external magnetic field and the direction of current in a conductor
The direction of Ampere's force is found according to the rule of the left hand. The wording of this rule is as follows. When the left hand is positioned in such a way that the lines of magnetic induction of the external field enter the palm, and four outstretched fingers indicate the direction of current flow in the conductor, while the thumb bent at a right angle will indicate the direction of the force that acts on the conductor element.
Figure 1 - left hand rule
Some problems arise when using the left hand rule if the angle between the field induction and the current is small. It is difficult to determine where the open palm should be. Therefore, for ease of application of this rule, the palm can be positioned so that it includes not the magnetic induction vector itself, but its module.
It follows from Ampère's law that the Ampere force will be zero if the angle between the line of magnetic induction of the field and the current is zero. That is, the conductor will be located along such a line. And the Ampere force will have the maximum possible value for this system if the angle is 90 degrees. That is, the current will be perpendicular to the line of magnetic induction.
Using Ampere's law, you can find the force acting in a system of two conductors. Imagine two infinitely long conductors that are at a distance from each other. Current flows through these conductors. The force acting from the side of the field created by the conductor with current number one on the conductor number two can be represented as.
Formula 2 - Ampere Force for two parallel conductors.
The force acting from the side of conductor number one on the second conductor will have the same form. Moreover, if the currents in the conductors flow in one direction, then the conductor will be attracted. If they are opposite, then they will repel. There is some confusion, because the currents flow in one direction, so how can they be attracted. After all, poles and charges of the same name always repel each other. Or Amper decided that it was not worth imitating the rest and came up with something new.
In fact, Ampère did not invent anything, because if you think about it, the fields created by parallel conductors are directed towards each other. And why they are attracted, the question no longer arises. To determine in which direction the field created by the conductor is directed, you can use the right screw rule.
Figure 2 - Parallel conductors with current
Using parallel conductors and the expression of the Ampere force for them, you can determine the unit of one Ampere. If the same currents with a force of one ampere flow through infinitely long parallel conductors located at a distance of one meter, then the interaction force between them will be 2 * 10-7 Newtons, for each meter long. Using this relationship, you can express what one ampere will be equal to.
This video talks about how a permanent magnetic field created by a horseshoe magnet affects a conductor with current. The role of the conductor with current in this case is performed by an aluminum cylinder. This cylinder lies on copper bars, through which an electric current is supplied to it. The force acting on a current-carrying conductor in a magnetic field is called the Ampère force. The direction of the Ampère force is determined using the left hand rule.
