One of the most important sections of modern physics is electromagnetic interactions and all definitions related to them. 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 is the foundation of the foundations
As children, 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 scientific language, you 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). This interaction is calledmagnetic force.
In general, it should be understood that any magnetic phenomena occur 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 the electric current.
Electric 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 very 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.
One 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 action, which itaffects moving particles and 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 occurs 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. Her absence would violate this principle.
There is nothing fundamental about the magnetic force - it is just a relativistic consequence of Coulomb's law.
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 the streetmagicians, they have become indispensable assistants in all their performances. Using the powers of magnetic stones, they were able 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 property of magnets, scientists invented the 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.
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. It was a thermal phenomenonelectric current. The students continued these experiments, and one of them noticed that the electric current has another interesting property. When 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, this creates a new opposite pole 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 greatly 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 to move a unit charge from point A0 to point A1.
The EMF is described by Faraday's laws, which are applied in three different physicalsituations:
- The conducted circuit moves in the generated uniform magnetic field. In this case, they speak of magnetic emf.
- The contour is at rest, but the source of the magnetic field itself is moving. This is already an electric emf phenomenon.
- Finally, the circuit and the source of the magnetic field are stationary, but the current that creates the magnetic field is changing.
Numerically, the EMF according to the Faraday formula is: EMF=W/q.
Consequently, the electromotive force is not a force in the literal sense, as 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 be 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 the law of conservation of momentum, which is why all problems in finding the Lorentz force should be solved based on it. Let's figure out howyou can determine the strength of the magnetic field.
Problems and examples of solutions
To find the force that arises around a conductor with current, you need to know several quantities: the charge, its speed and the value of the induction of the emerging 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 90o, since a 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 1.610-19 Cl. Next, we calculate the force using the formula: 1, 610-19100, 21 (the sine of the right angle is 1)=3, 210- 19 Newtons.