Today we will explain why light radiation is the most important concept in modern physics. The properties of quanta of electromagnetic energy and the history of their study will also be described.
Sun and moon
In world culture, there are many myths about the origin and behavior of the main heavenly bodies. Somewhere they are brother and sister, somewhere - husband and wife, some people believe that these are the fruits of the world tree, some - that they are precious stones and gods. And all the legends were created in an attempt to understand why light radiation is a product of the sun and moon.
Often discoveries happen by chance, and the path of science is far from as direct as it seems. For example, for an initial understanding of the dance of celestial bodies, a religion was needed, which first forbade the investigation of the phenomenon, and then she herself asked scientists about it.
Easter and quantum
In the sixteenth century, Pope Leo X decided to improve the tables to calculate the date of Easter. It is incredibly difficult to understand exactly when this day is coming, because you need to connect three different time frames: days of the week, solar and lunar cycles.
- Easter is certainly Sunday.
- The holiday always comes after the vernal equinox.
- It is important that the full moon has already passed by the time Easter arrives.
- Another condition was the mismatch of the Jewish, Catholic and Orthodox traditions.
Now this day can be predicted for a millennium ahead, but before the tables for the calculation were valid for five to six years, and then it was necessary to carry out a new adjustment of the dates. Such low accuracy was associated with the full confidence of civilized people that the Earth is flat, located in the center of the universe, and the visible changes in the planets, the Sun and the Moon were explained by the presence of epicycles, small additional circles on which celestial bodies rotate.
All this brought a lot of trouble in the calculations. In order not to bother with this every time, Leo X ordered a study from astronomers of that time. And they came to an amazing discovery: the Earth is not the center of the universe, the source of light radiation is the Sun, and the Moon only reflects light and is itself something like a planet. An ancient study further led to an understanding of the electromagnetic and quantum nature of light.
Newton and Faraday
In the seventeenth and eighteenth centuries, the English scientist Isaac Newton wondered: "What is a sunbeam?" Schoolchildren know him as the author of the law of gravity, but he also studied optics. As a result, Newton came to the conclusion that the light waves of the radiation of the Sun are decomposed into color components, that is, they turn into a rainbow. And thereby laid the foundation for understanding the wave nature of light.
And in the twentieth year of the nineteenth century, the English physicist Michael Faraday proved: current (and in general any moving charged object) is a source of an electromagnetic field. To understand that light radiation is a quantum of an electromagnetic field, it was necessary to invent a fundamentally new physics of the world of elementary particles.
Plank and Schrödinger Cat
The era of quantum began with the study of heated bodies. From classical physics, it was known that thermal radiation is continuous. The maximum of this spectrum was associated with body temperature by the Rayleigh-Jeans formula. She described the experimental data well at small wavelengths, but problems began in the blue region of the spectrum: the energy of any object was so great that it could destroy the universe. This phenomenon is called ultraviolet disaster.
In 1900, Max Planck tried to write such a formula for the energy of light radiation from a heated body, excluding the scenario of the destruction of the world. At the same time, the German physicist was forced to introduce a quantity that he called the quantum of action. And this term denoted the smallest portion of the electromagnetic field.
Planck himself considered quantum to be nothing more than a mathematical ploy, but other scientists realized the potential of such a discovery. A whole school of researchers (among them were Albert Einstein, Erwin Schrödinger, Werner Karl Heisenberg) created a new direction in science - quantum physics. Thanks to them, people finally understood why atoms emit and what is light.
However, Max Planck for a long time did not accept the fundamental nature of his discovery. He argued with colleagues and even came up with a paradox with Schrödinger's cat, which is alive and dead at the same time. For some time, the scientist tried to circumvent a quantum in the formula of the radiation of an absolutely black body with various mathematical tricks. But nothing came of it, and in the end he gave up.
What is light?
Thanks to the activities of these wonderful and courageous scientists, we now know that light is a quantum of electromagnetic radiation that has the properties of both a wave and a material particle.
- The wavelength of light radiation is the distance between two adjacent maxima of the electromagnetic field. It is denoted by the letter λ. Generally speaking, this is the distance between the identical phases of neighboring oscillations of a single wave. But in the figure it is more clearly possible to demonstrate precisely the distance between the "humps" or "hollows." The wavelength is measured in meters with the appropriate prefix. For example, visible radiation is quanta with λ from 380 to 780 nanometers (nm).
- The frequency of light radiation is the number of waves that fit in a unit of time (per second). This characteristic is more temporary than spatial. It is denoted by the Greek symbol ν or the Latin letter f .
- The amplitude of electromagnetic oscillations is the height of the maximums and minimums of the oscillation. In the general case, it shows the intensity of electric and magnetic fields that are bent in mutually perpendicular planes.
- The mass of a particle is the reason that light has an impulse. This characteristic confirms: a quantum of the electromagnetic field (called a photon) is a particle! True, do not forget that her rest mass is zero, which means that she exists only in motion.
The frequency and wavelength of light is related by the relation λν = c, where c is the speed of light in vacuum. The lower the wavelength and the higher the frequency, the higher the wave energy.
One or many?
If we consider one photon, then it will possess all the characteristics described above. But there are effects and quantities that arise only when it comes to mass effect.
For example, anyone knows: at sunset, the intensity of sunlight is less. At this time, you can calmly look at the disk of the central luminary with unprotected eyes. While it is dangerous to even look at the zenith at the sun , you can go blind for a moment and lose orientation in space. And the reason for this is the curvature of our planet. The lower the sun sets, the thicker the atmosphere passes its rays, and the more they are absorbed.
At the same time, less and less photons get to the surface of the earth. This phenomenon can be described by a change in the power of light radiation.
Luminous flux and the human eye
At the same time, the luminous flux is a completely specific physical term. And now we will reveal its meaning.
The more photons per square meter of area per unit time, the greater the radiation flux power.
If the number of light quanta is recorded by an impartial machine, it will show the correct value from the point of view of physics. But the human eye has a maximum, which he sees most well, and all other frequencies, vision catches worse. That is, people see less red and violet photons than they fall to the surface, but green ones are perceived better. So, the luminous flux is the flux of radiation, which is adjusted for the spectral sensitivity of the human eye.
Nuclear reactor and explosion
Any science has a reverse, dark side. As soon as the mechanical block was invented, it began to be used to create throwing machines. As soon as chemists advanced in the study of matter, their knowledge began to be used against people. And the atom increased the power of human combat capabilities to the complete destruction of itself and the planet.
As you know, a vigorous reaction is the source of many types of particles and radiation. Even a very pure chemical radioactive substance produces neutrons, alpha, beta, gamma radiation, as well as electromagnetic waves of all ranges. The light radiation from the explosion affects much more directly the shock wave. Burns are treated for a long time and leave scars. Only the radioactive component of this act of inhumanity, the explosion of an atomic bomb, causes more serious damage to living matter.