Albert Einstein is probably known to every inhabitant of our planet. It is known thanks to the famous formula for the connection between mass and energy. However, he did not receive the Nobel Prize for it. In this article, we will consider two Einstein formulas that turned the physical ideas about the world around us at the beginning of the 20th century.
Einstein's fruitful year
In 1905, Einstein published several articles at once, which mainly de alt with two topics: the theory of relativity he developed and the explanation of the photoelectric effect. The materials were published in the German journal Annalen der Physik. The very titles of these two articles caused bewilderment in the circle of scientists at that time:
- "Does the inertia of a body depend on the energy it contains?";
- "A heuristic point of view on the origin and transformation of light".
In the first, the scientist cites the currently known formula of Einstein's theory of relativity, which combinesuniform equality of mass and energy. The second article provides an equation for the photoelectric effect. Both formulas are currently used both to work with radioactive matter and to generate electrical energy from electromagnetic waves.
Short formula of special relativity
The theory of relativity developed by Einstein considers the phenomena when the masses of objects and their speeds of movement are huge. In it, Einstein postulates that it is impossible to move faster than light in any frame of reference, and that at near-light speeds, the properties of space-time change, for example, time begins to slow down.
The theory of relativity is difficult to understand from a logical point of view, because it contradicts the usual ideas about motion, the laws of which were established by Newton in the 17th century. However, Einstein came up with an elegant and simple formula from complex mathematical calculations:
E=mc2.
This expression is called Einstein's formula for energy and mass. Let's figure out what it means.
The concepts of mass, energy and the speed of light
To better understand Albert Einstein's formula, you should 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 matter 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 certainspeed. Mass is measured in kilograms.
The issue of energy is also not simple. So, there are a variety of its manifestations: light and thermal, 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 is capable of moving bodies against the action of other external forces. The SI measure is the joule.
What is the speed of light is approximately clear to everyone. It is understood as the distance that an electromagnetic wave travels per unit of time. For vacuum, this value is a constant; in any other real 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 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 m to E and back 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 occurring in closed systems. Einstein showed that this is not the case, and these phenomena persist not separately, but together.
Another feature of Einstein's formula or the law of equivalence of mass and energy is the coefficient of proportionality between these quantities,i.e. c2. It is approximately equal to 1017 m2/s2. This huge value suggests that even a small amount of mass contains huge reserves of energy. For example, if you follow this formula, then just one dried grape (raisin) can satisfy all the energy needs of Moscow in one day. On the other hand, this huge factor also explains why we don't observe mass changes in nature, because they are too small for the energy values we use.
The influence of the formula on the course of the history of the 20th 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 the disappearance of mass. A striking example is the fission of the uranium nucleus. If we add up the mass of the light isotopes formed after this fission, then it will turn out to be much less than that for the original nucleus. Disappeared mass turns into energy.
Human ability to use atomic energy led to the creation of a reactor that serves to provide electricity to the civilian population of cities, and to the design of the deadliest weapon in all known history - the atomic bomb.
The appearance of the first atomic bomb in the United States ended the Second World War against Japan ahead of schedule (in 1945, the United States dropped these bombs on two Japanese cities), and also became the main deterrent to the outbreak of the Third World War.
Einstein himself, of course, could notto foresee such consequences of the formula he discovered. Note that he did not take part in the Manhattan project to create atomic weapons.
The phenomenon of the photoelectric effect and its explanation
Now let's move on to the question for which Albert Einstein was awarded the Nobel Prize in the early 1920s.
The phenomenon of 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, which was established at the beginning of the 20th century. Thus, it was not clear why the photoelectric effect is observed without a time delay (less than 1 ns), why the decelerating potential does not depend on the intensity of the light source. Einstein gave a brilliant explanation.
The scientist suggested a simple thing: when light interacts with matter, it behaves not like a wave, but like a corpuscle, a quantum, a bunch of energy. The initial concepts were already known - the corpuscular theory was proposed by Newton in the middle of the 17th century, and the concept of electromagnetic wave quanta was introduced by compatriot physicist Max Planck. Einstein was able to bring together all the knowledge of theory and experiment. He believed that a photon (quantum of light), interacting with just one electron, completely gives it its energy. If this energy is large enough to break the bond between the electron and the nucleus, then the charged elementary particle opens from the atom and goes into a free state.
Tagged Viewsallowed Einstein to write down the formula for the photoelectric effect. We will consider it in the next paragraph.
Photoelectric effect and its equation
This equation is a bit longer than the famous energy-mass relation. It looks like this:
hv=A + Ek.
This equation or Einstein's formula for the photoelectric effect reflects the essence of what is happening in the process: a photon with energy hv (Planck's constant multiplied by the oscillation frequency) is spent on breaking the bond between the electron and the nucleus (A is the work function of the electron) and on communicating a negative particle of kinetic energy (Ek).
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 being applied to convert light energy into electricity thanks to solar panels.
They use an internal photoelectric effect, that is, the electrons "pulled out" from the atom do not leave the material, but remain in it. The active substance is n- and p-type silicon semiconductors.
