Albert Einstein, perhaps, is known to every inhabitant of our planet. They know him thanks to the famous formula of the connection of mass and energy. Nevertheless, he received the Nobel Prize not for her. In this article, we consider two Einstein's formulas that turned over the physical notions of the world around us at the beginning of the 20th century.
The fruitful year of Einstein
In 1905, Einstein published several articles at once, which mainly dealt with two topics: his theory of relativity and an explanation of the photoelectric effect. Materials were published in the German journal Annalen der Physik. The very names of these two articles caused bewilderment among scientists at that time:
- "Does the inertia of the body depend on the energy contained in it?";
- "Heuristic point of view about the origin and transformation of light."
In the first, the scientist cites Einstein's theory of relativity, which is now known to everyone, which combines mass and energy into a single equality. The second article provides an equation for the photoelectric effect. Both formulas are currently used both for working with radioactive matter and for generating electric energy from electromagnetic waves.
Short formula of the special theory of relativity
The theory of relativity developed by Einstein considers phenomena when the masses of objects and their speed of movement are huge. In it, Einstein postulates that it is impossible to move faster than light in any reference frame, and that at near-light speeds there is a change in the properties of space-time, for example, time begins to slow down.
The theory of relativity is difficult to understand from a logical point of view, since it contradicts the usual notions of motion, the laws of which were established by Newton in the 17th century. Nevertheless, Einstein from complex mathematical calculations came to an elegant and simple formula:
E = m * c 2 .
This expression is called the Einstein formula for energy and mass. Let’s figure out what it means.
Concepts of mass, energy and speed of light
In order to better understand Albert Einstein’s formula, you need to understand in detail the meaning of each symbol that is present in it.
Let's start with the mass. You can often hear that this physical quantity is related to the amount of substance contained in the body. This is not entirely true. It is more correct to define mass as a measure of inertia. The larger the body, the harder it is to give it a certain speed. Mass is measured in kilograms.
The issue of energy is also not simple. So, there are its most diverse manifestations: light and heat, steam and electric, kinetic and potential, chemical bonds. All these types of energy are united by one important property - their ability to do work. In other words, energy is a physical quantity that can move bodies against the action of other external forces. A measure in the SI system is the joule.
What is the speed of light, roughly understandable to everyone. By it is meant the distance that an electromagnetic wave travels per unit of time. For vacuum, this value is a constant; in any other material medium, it decreases. The speed of light is measured in meters per second.
The meaning of Einstein's formula
If you look closely at this simple formula, you can see that the mass is related to energy through a constant (the square of the speed of light). Einstein himself explained that mass and energy are manifestations of the same thing. In this case, transitions of m to E and vice versa are possible.
Before the advent of Einstein's theory, scientists believed that the laws of conservation of mass and energy exist separately and are valid for any processes that occur in closed systems. Einstein showed that this is not so, and these phenomena persist not separately, but together.
Another feature of the Einstein formula or the law of equivalence of mass and energy is the coefficient of proportionality between these quantities, that is, c 2 . It is approximately 10 17 m 2 / s 2 . This huge value suggests that even a small amount of mass contains huge reserves of energy. For example, if you follow this formula, then only one dried grape berry (raisins) can satisfy all the energy needs of Moscow in one day. On the other hand, this huge coefficient also explains why we do not observe mass changes in nature, because they are too small for the energy values used by us.
The influence of the formula on the course of history of the XX century
Thanks to the knowledge of this formula, a person was able to master atomic energy, the huge reserves of which are explained by the processes of mass disappearance. A striking example is the fission of the nucleus of uranium. If we add up the mass of light isotopes formed after this fission, then it will be much less than that for the original nucleus. The disappeared mass passes into energy.
The human ability to use atomic energy has led to the creation of a reactor, which serves to provide electricity to the civilian population of cities, and to the construction of the deadliest weapon in the entire history of the atomic bomb.
The appearance of the first atomic bomb in the United States prematurely ended the Second World War against Japan (in 1945, the United States dropped these bombs on two Japanese cities), and also became the main deterrent to the Third World War.
Einstein himself, of course, could not foresee such consequences of the formula he discovered. Note that he did not participate in the Manhattan project to create atomic weapons.
The phenomenon of the photoelectric effect and its explanation
Now we turn to the consideration of the question, for the answer to which Albert Einstein was awarded the Nobel Prize in the early 1920s.
The photoelectric effect, discovered in 1887 by Hertz, consists in the appearance of free electrons above the surface of a certain material if it is irradiated with light of certain frequencies. It was not possible to explain this phenomenon from the point of view of the wave theory of light, established at the beginning of the 20th century. So, it was unclear why the photoelectric effect is observed without a time delay (less than 1 ns), why the inhibitory potential does not depend on the intensity of the light source. Einstein gave a brilliant explanation.
The scientist suggested a simple thing: light when interacting with matter does not behave like a wave, but like a corpuscle, quantum, clot of energy. The initial concepts were already known - the particle theory was proposed by Newton in the middle of the XVII century, and the concept of the quanta of electromagnetic waves was introduced by compatriot physicist Max Planck. Einstein was able to put together all the knowledge of theory and experiment. He believed that a photon (quantum of light), interacting with just one electron, completely gives him his energy. If this energy is large enough to break the bond between the electron and the nucleus, then a charged elementary particle opens from the atom and goes into a free state.
The marked performances allowed Einstein to write down the formula for the photoelectric effect. We consider it in the next paragraph.
The photoelectric effect and the equation for it
This equation is slightly longer than the famous relationship of energy and mass. It has the following form:
h * v = A + E k.
This Einstein’s equation or formula for the photoelectric effect reflects the essence of what is happening in the process: a photon with energy h * v (Planck’s constant times the frequency of oscillations) is used to break the bond between the electron and the nucleus (A is the electron work function) and to communicate a negative particle of kinetic energy (E k ).
The above formula made it possible to explain all the mathematical dependences observed in experiments on the photoelectric effect and led to the formulation of the corresponding laws for the phenomenon under consideration.
Where is the photoelectric effect used?
Currently, Einstein's ideas outlined above are used to convert light energy into electricity through solar panels.
They use the internal photoelectric effect, that is, the electrons "torn out" of the atom do not leave the material, but remain in it. Silicon semiconductors of n- and p-type are used as the active substance.