Physics of electricity: definition, experiments, unit of measurement

The physics of electricity is what every one of us has to face. In the article we will consider the basic concepts associated with it.

What is electricity? For an uninitiated person, it is associated with a flash of lightning or with energy feeding the TV and the washing machine. He knows that electric trains use electrical energy. What else can he tell? About our dependence on electricity, it is reminiscent of power lines. Someone will be able to give a few other examples.

However, many other, not so obvious, but everyday phenomena are connected with electricity. With all of them we are introduced by physics. Electricity (tasks, definitions and formulas) we begin to study in school. And we learn a lot of interesting things. It turns out that a beating heart, a running athlete, a sleeping child and a floating fish - all produce electrical energy.

Electrons and protons

Let's define the basic concepts. From the scientist's point of view, the physics of electricity is associated with the motion of electrons and other charged particles in various substances. Therefore, the scientific understanding of the nature of the phenomenon of interest to us depends on the level of knowledge about atoms and the constituent subatomic particles. The key to this understanding is a tiny electron. The atoms of any substance contain one or more electrons moving in different orbits around the nucleus just as planets revolve around the Sun. Usually the number of electrons in an atom is equal to the number of protons in the nucleus. However, protons, being much heavier than electrons, can be regarded as fixed in the center of the atom. This extremely simplified model of the atom is quite enough to explain the basics of such a phenomenon as the physics of electricity.

What else do I need to know? Electrons and protons have the same electrical charge (but of different sign), so they are attracted to each other. The proton charge is positive, and the electron charge is negative. An atom having more or less electrons than usual is called an ion. If there are not enough of them in the atom, it is called a positive ion. If it contains their excess, it is called a negative ion.

When an electron leaves an atom, it acquires a certain positive charge. An electron, devoid of its opposite - a proton, either moves to another atom, or returns to the former.

Why do electrons leave atoms?

There are several reasons for this. The most common is that under the action of a light pulse or some external electron, an electron moving in an atom can be knocked out of its orbit. Heat causes atoms to oscillate faster. This means that electrons can fly out of their atom. In chemical reactions, they also move from atom to atom.

A good example of the relationship between chemical and electrical activity gives us muscle. Their fibers are reduced by the action of an electrical signal coming from the nervous system. Electric current stimulates chemical reactions. They are what lead to muscle contraction. External electrical signals are often used to artificially stimulate muscle activity.

Conductivity

In some substances, electrons under the action of an external electric field move more freely than in others. It is said that such substances have good conductivity. They are called conductors. These include most metals, heated gases and some liquids. Air, rubber, oil, polyethylene and glass do not conduct electricity well. They are called dielectrics and are used to insulate good conductors. Ideal insulators (absolutely non-conducting current) do not exist. Under certain conditions, electrons can be removed from any atom. However, usually these conditions are so difficult to fulfill that from a practical point of view, such substances can be considered non-conductive.

Getting acquainted with such a science as physics (section "Electricity"), we learn that there is a special group of substances. These are semiconductors. They behave in part as dielectrics, and partly as conductors. These include, in particular, germanium, silicon, copper oxide. Due to its properties, the semiconductor finds many applications. For example, it can serve as an electric valve: like a bicycle tire valve, it allows charges to move only in one direction. Such devices are called rectifiers. They are used in miniature radio receivers, and at large power plants to convert AC to DC.

Heat is a chaotic form of motion of molecules or atoms, and temperature is a measure of the intensity of this movement (for most metals with a decrease in temperature, the movement of the electrons becomes more free). This means that the resistance to free movement of electrons decreases with decreasing temperature. In other words, the conductivity of metals increases.

Superconductivity

In some substances, at very low temperatures, the resistance to the flow of electrons disappears completely, and the electrons, having started the motion, continue it unlimitedly. This phenomenon is called superconductivity. At a temperature of several degrees above absolute zero (-273 ° C), it is observed in metals such as tin, lead, aluminum, and niobium.

Generators Van de Graaf

The school curriculum includes various experiments with electricity. There are several kinds of generators, one of which we would like to tell in more detail. The Van de Graaf generator is used to generate ultrahigh voltages. If an object containing an excess of positive ions is placed inside the container, then on the inner surface of the latter there will appear electrons, and on the outside - the same number of positive ions. If we now touch the inner surface of a charged object, then all free electrons will pass to it. On the outside, however, the positive charges remain.

In the Van de Graaf generator, positive ions from the source are applied to the conveyor belt passing inside the metal sphere. The tape is connected to the inner surface of the sphere by means of a conductor in the form of a comb. Electrons drain from the inner surface of the sphere. On the outside, positive ions appear. The effect can be enhanced by using two generators.

Electricity

In the school course of physics there is also such a thing as electric current. What is it? The electric current is due to the movement of electric charges. When the electric lamp connected to the battery is turned on, the current flows along the wire from one pole of the battery to the lamp, then through its hair, causing it to glow, and returns back along the second wire to the other pole of the battery. If the switch is turned, the circuit will open - the current will stop and the lamp will go out.

Motion of electrons

The current in most cases is an ordered motion of electrons in a metal serving as a conductor. In all conductors and some other substances, some random movement always occurs, even if the current does not flow. Electrons in matter can be relatively free or strongly bound. Good conductors have free electrons that can move. But in poor conductors, or insulators, most of these particles are sufficiently tightly connected with atoms, which impedes their movement.

Sometimes a natural or artificial way in the conductor creates a movement of electrons in a certain direction. This flow is called an electric current. It is measured in amperes (A). Current carriers can also be ions (in gases or solutions) and "holes" (lack of electrons in certain types of semiconductors, which behave as positively charged carriers of electric current.) In order to force electrons to move in one direction or another, some force is needed. Its sources can be: exposure to sunlight, magnetic effects and chemical reactions, some of which are used to generate an electric current, usually for this purpose: a generator using magnetic effects, and Element (battery), the action of which is due to chemical reactions.These two devices, creating an electromotive force (EMF), cause the electrons to move in one direction along the circuit.The magnitude of the EMF is measured in volts (V). These are the basic units of measurement of electricity.

The magnitude of the EMF and the current strength are related to each other like pressure and flow in a liquid. Water pipes are always filled with water under a certain pressure, but water starts to flow only when the tap is opened.

Similarly, the electrical circuit can be connected to the source of EMF, but the current in it will not flow until a path is created along which the electrons can move. They can be, say, an electric lamp or a vacuum cleaner, the switch here plays the role of a tap that "lets out" the current.

The relationship between current and voltage

As the voltage in the circuit rises, the current also increases. Studying the course of physics, we learn that the electrical circuits consist of several different sections: usually it is a switch, conductors and the device is a consumer of electricity. All of them, connected together, create resistance to the electric current, which (under the condition of constant temperature) for these components does not change with time, but for each of them is different. Therefore, if the same voltage is applied to a light bulb and to an iron, the flow of electrons in each of the instruments will be different, since their resistances are different. Consequently, the current flowing through a certain section of the circuit is determined not only by the voltage, but also by the resistance of the conductors and devices.

Ohm's law

The magnitude of the electrical resistance is measured in ohms (Ohms) in a science such as physics. Electricity (formulas, definitions, experiments) is an extensive topic. We will not derive complex formulas. For the first acquaintance with the topic, it is enough that it was said above. However, one formula is still worth withdrawing. It's quite simple. For any conductor or system of conductors and devices, the relationship between voltage, current and resistance is given by the formula: voltage = current x resistance. This is the mathematical expression of Ohm's law, named after George Ohm (1787-1854), who first established the relationship of these three parameters.

The physics of electricity is a very interesting section of science. We have considered only the basic concepts associated with it. You have learned what electricity is, how it is formed. We hope that this information will be useful to you.