The physics of electricity is something that each of us has to deal with. 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 the energy that feeds the TV and washing machine. He knows that electric trains use electrical energy. What else can he say? Power lines remind him of our dependence on electricity. Someone can give a few other examples.
However, many other, not so obvious, but everyday phenomena are connected with electricity. Physics introduces us to all of them. We begin to study electricity (tasks, definitions and formulas) at school. And we learn a lot of interesting things. It turns out that a beating heart, a running athlete, a sleeping baby and a swimming fish all generate electrical energy.
Electrons and protons
Let's define the basic concepts. From the point of view of a scientist, the physics of electricity is associated with the movement 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 their constituent subatomic particles. The tiny electron is the key to this understanding. The atoms of any substance contain one or more electrons that move in various orbits around the nucleus, just as the 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 considered as if fixed in the center of the atom. This extremely simplified model of the atom is enough to explain the basics of such a phenomenon as the physics of electricity.
What else do you need to know? Electrons and protons have the same electrical charge (but different sign), so they are attracted to each other. The charge of a proton is positive and that of an electron is negative. An atom that has more or less electrons than usual is called an ion. If there are not enough of them in an atom, then it is called a positive ion. If it contains an excess of them, then it is called a negative ion.
When an electron leaves an atom, it acquires some positive charge. An electron, deprived of its opposite - a proton, either moves to another atom, or returns to the previous one.
Why do electrons leave atoms?
This is due to several reasons. The most general is that under the influence of a pulse of light or some external electron, an electron moving in an atom can be knocked out of its orbit. Heat makes the atoms vibrate faster. This means that electrons can fly out of their atom. In chemical reactions, they also move from atom toatom.
A good example of the relationship between chemical and electrical activity is provided by our muscles. Their fibers contract when exposed to an electrical signal from the nervous system. Electric current stimulates chemical reactions. They 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. Such substances are said to have good conductivity. They are called conductors. These include most metals, heated gases, and some liquids. Air, rubber, oil, polyethylene and glass are poor conductors of electricity. They are called dielectrics and are used to insulate good conductors. Ideal insulators (absolutely non-conductive) do not exist. Under certain conditions, electrons can be removed from any atom. However, these conditions are usually so difficult to meet 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 partly 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, itallows charges to move in only one direction. Such devices are called rectifiers. They are used in miniature radios and large power plants to convert AC to DC.
Heat is a chaotic form of movement of molecules or atoms, and temperature is a measure of the intensity of this movement (for most metals, with decreasing temperature, the movement of electrons becomes freer). This means that the resistance to the 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 moving, continue it indefinitely. This phenomenon is called superconductivity. At temperatures a few degrees above absolute zero (-273 °C), it is observed in metals such as tin, lead, aluminum and niobium.
Van de Graaff generators
The school curriculum includes various experiments with electricity. There are many types of generators, one of which we would like to talk about in more detail. The Van de Graaff generator is used to produce ultra-high voltages. If an object containing an excess of positive ions is placed inside a container, then electrons will appear on the inner surface of the latter, and the same number of positive ions will appear on the outer surface. If we now touch the inner surface with a charged object, then all free electrons will pass to it. On the outsidepositive charges will remain.
In a Van de Graaff generator, positive ions from a source are applied to a conveyor belt inside a metal sphere. The tape is connected to the inner surface of the sphere with the help of a conductor in the form of a comb. The electrons flow down from the inner surface of the sphere. Positive ions appear on its outer side. The effect can be enhanced by using two generators.
Electric current
The school physics course also includes such a thing as electric current. What is it? Electric current is due to the movement of electric charges. When an electric lamp connected to a battery is turned on, current flows through a wire from one pole of the battery to the lamp, then through its hair, causing it to glow, and back through the second wire to the other pole of the battery. If the switch is turned, the circuit will open - the current flow will stop and the lamp will go out.
Movement of electrons
Current in most cases is an ordered movement of electrons in a metal that serves as a conductor. In all conductors and some other substances there is always some random movement going on, even if there is no current flowing. Electrons in matter can be relatively free or strongly bound. Good conductors have free electrons that can move around. But in poor conductors, or insulators, most of these particles are strongly enough connected with atoms, which prevents their movement.
Sometimes, naturally or artificially, the movement of electrons in a certain direction is created in a conductor. This flow is called electric current. It is measured in amperes (A). Ions (in gases or solutions) and “holes” (lack of electrons in some types of semiconductors) can also serve as current carriers. The latter behave like positively charged electric current carriers. Some force is needed to make electrons move in one direction or another. In nature its sources can be: exposure to sunlight, magnetic effects and chemical reactions. Some of them are used to generate electricity. Usually for this purpose are: a generator using magnetic effects, and a cell (battery) whose action is due to chemical reactions. Both devices, creating an electromotive force (EMF), causes the electrons to move in one direction through the circuit. The EMF value is measured in volts (V). These are the basic units of electricity.
The magnitude of the EMF and the strength of the current are interconnected, like pressure and flow in a liquid. Water pipes are always filled with water at a certain pressure, but water only starts flowing when the faucet is turned on.
Similarly, an electric circuit can be connected to a source of EMF, but current will not flow in it until a path is created for the electrons to move along. It can be, say, an electric lamp or a vacuum cleaner, the switch here plays the role of a tap that “releases” current.
The relationship between current andvoltage
As the voltage in the circuit increases, so does the current. Studying a physics course, we learn that electrical circuits consist of several different sections: usually a switch, conductors and a device that consumes electricity. All of them, connected together, create a resistance to electric current, which (assuming a constant temperature) for these components does not change with time, but is different for each of them. Therefore, if the same voltage is applied to a light bulb and to an iron, then the flow of electrons in each of the devices will be different, since their resistances are different. Therefore, the strength of the current flowing through a certain section of the circuit is determined not only by voltage, but also by the resistance of conductors and devices.
Ohm's Law
The value of electrical resistance is measured in ohms (Ohm) in a science such as physics. Electricity (formulas, definitions, experiments) is a vast topic. We will not derive complex formulas. For the first acquaintance with the topic, what has been said above is enough. However, one formula is still worth deriving. She is quite uncomplicated. 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 between these three parameters.
Physics of electricity is a very interesting branch of science. We have considered only the basic concepts associated with it. Did you knowWhat is electricity and how is it generated? We hope you find this information useful.
