One of the most important sections of modern physics is electromagnetic interactions and all the definitions associated with them. It is this interaction that explains all the electrical phenomena. The theory of electricity covers many other areas, including optics, because 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
In childhood, adults showed us various tricks using magnets. These amazing figures, which are attracted to each other and can attract small toys, have always pleased the children's eye. What are magnets and how does magnetic force affect iron parts?
Explaining the scientific language, you have to turn to one of the basic laws of physics. According to the Coulomb law and the special theory of relativity, a certain force acts on a charge, which directly proportionally depends on 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 magnetic phenomena occur only when the charges move inside the conductor or in the presence of currents in them. In the study of magnets and the very definition of magnetism, it should be understood that they are closely interconnected with the phenomenon of electric current. Therefore, let's understand the essence of electric current.
Electric force is the force that acts between an electron and a proton. It is numerically much larger than the value of gravitational force. It is generated by an electric charge, or rather, by its movement inside the conductor. The charges, in turn, are of two types: positive and negative. As you know, positively charged particles are attracted to negatively charged. However, charges of the same sign have the property of repelling.
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 a current in a magnetic field is called the Ampere force and is found by the rule of the "left hand".
Empirical evidence
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 eyes. It is possible to trace it only by its action, which it exerts on moving particles and on magnetized bodies.
The force acting on a conductor with a current 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, the laws of Ampere are defined as the rules of the "left" and "right" hands.
Magnetic field characteristics
It should be understood that a magnetic field always arises not only around sources of electric current, but also around magnets. It is usually depicted using magnetic field lines. Graphically, it looks as if a sheet of paper were put on a magnet, and sawdust of iron was poured on top. They will take exactly the same form as in the picture below.
In many popular books on physics, magnetic force is introduced as a result of experimental observations. It is considered a separate fundamental force of nature. Such a representation is erroneous; in fact, the existence of magnetic force follows from the principle of relativity. Its absence would lead to a violation of this principle.
There is nothing fundamental in magnetic force — it is simply a relativistic consequence of Coulomb's law.
The use of magnets
According to 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 things 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 assistants in all their performances. Using the power of magnetic stones, they were able to create a whole fantastic show that attracted many viewers.
As the stones spread throughout all parts of the world, legends and various myths began to circulate about them. Once the stones were 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 was noticed that if you put magnetic iron ore on a wooden float, fix it, and then rotate it, then it will try to return to its original position. Simply put, the magnetic force acting on it will rotate the iron ore in a certain way.
Using this property of magnets, scientists have come up with a compass. On the round shape made of wood or cork, two main poles were drawn and a small magnetic arrow 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 ordinary tourists who like to explore desert and mountainous areas.
Interesting experiences
The scientist Hans Oersted devoted almost his entire life to electricity and magnets. Once 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 warmed up and began to bend. This was a phenomenon of the thermal property of electric current. Students continued these experiments, and one of them noticed that electric current has another interesting property. When current flowed in the conductor, the arrow of the compass next to it began to gradually deviate. 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 made attempts to find a magnetic charge, but an isolated magnetic pole could not be detected. This is explained by the fact that, unlike electric, magnetic charges do not exist. After all, otherwise it would be possible to separate the 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 Ampere currents. It turns out that the magnet can be considered as a metal rod along which direct current circulates. It is for this reason that introducing an iron core into the solenoid significantly increases the magnetic field.
Magnet or EMF energy
Like any physical phenomenon, a magnetic field has the energy that it expends to move the charge. There is the concept of EMF (electromotive force), it is defined as the work of moving a single charge from point A 0 to point A 1 .
It is described by EMF by the laws of Faraday, which are used in three different physical situations:
- The conducted circuit moves in a uniform magnetic field. In this case, they talk about magnetic EMF.
- The circuit is at rest, but the source of the magnetic field itself is moving. This is a phenomenon of electric emf.
- And finally, the circuit and the source of the magnetic field are motionless, but the current that creates the magnetic field changes.
Numerically, the EMF by the Faraday formula is: EMF = W / q.
Therefore, the electromotive force is not literally a force, since it is measured in Joules on the Coulomb or in Volts. It turns out that it represents the energy that is communicated to the conduction electron bypassing the circuit. Each time, making the next round of the rotating frame of the generator, the electron acquires energy, numerically equal to the EMF. This additional energy can not only be transferred during collisions of atoms of the external 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 moduli of the velocity 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 commonly called the Lorentz force. An interesting fact is that Newton’s 3rd law is not valid for this force. It obeys only the law of conservation of momentum, which 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 emerging magnetic field. The next task 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 ° , since a charged particle moves perpendicular to the lines of induction). The solution comes down to finding a charge. Glancing at the poison table, we find that the proton has a charge of 1.6 * 10 -19 C. Next, we calculate the force by the formula: 1.6 * 10 -19 * 10 * 0.2 * 1 (the sine of the right angle is 1) = 3.2 * 10 -19 Newtons.