Today we will talk about the essence of such a phenomenon of optics as a monochromatic wave. We consider in detail the properties of light vibrations and the electromagnetic scale.
Light, wind, sea, sand
These four ingredients are the perfect recipe for a good vacation. But now it’s not about summer holidays, but about physics. Light, wind, the surface of water and sand have one thing in common - vibrations. The case of the wind is special: the oscillations do not occur up and down - rather, it is a change in density according to the “rarefaction-condensation” type. And when a person feels the touch of a light breeze on his face, then this denser part of the Earth’s air atmosphere tends to take a more rarefied state, dumping excess mass into the region of lower pressure.
With sea and sand, everything is easier. Fluctuations of the medium are visible, one and the same surface area oscillates in space. A piece of paper thrown into the sea or river in the absence of a current will rise and fall, but will not be able to swim to the shore.
Electromagnetic vibrations, which include a monochromatic light wave, oscillate in space in the same way. But in addition to the direction of propagation, when moving through space, a quantum of light generates an amplitude vector, a wave vector and an electric and magnetic field intensity vector. All of them have rigidly set angles with respect to each other and oscillate together with the wave front. So a monochromatic wave is a whole package of energy with many properties that propagate in space in different ways.
Properties of electromagnetic radiation as a substance: mass and momentum
At the beginning of the twentieth century, scientists had to admit that any elementary particles possess both the properties of a wave and the characteristics of a material particle. The experiments on the pressure of light, which were made by the Russian scientist Lebedev, proved that light is capable of transmitting momentum, and therefore has mass. But any reference will explain that the mass of a photon at rest is zero. Its mass is, as it were, “smeared” into a packet of energy. Faced with a substance, light changes its properties (for example, heats), and at the same time loses its individuality and essence.
Properties of electromagnetic radiation as waves: frequency, length, amplitude, phase
But in order to determine the wavelength of monochromatic light, you only need to know about its wave properties. These characteristics include:
- Frequency. It is denoted by the Greek letter ν if the frequency is linear, and ω if it is cyclic. It is defined as the number of waves that "fit" in a certain period of time. This is a temporary characteristic of electromagnetic radiation.
- Wavelength. It is designated as λ. Determines the distance between the same phases of two adjacent waves, for example, between two maxima. This is the spatial characteristic of electromagnetic radiation. The frequency and wavelength are inversely proportional to each other. That is, the higher the frequency, the shorter the wavelength.
- Amplitude. It can be designated in different ways, but the Latin symbol A is most often found. This is the height of the “humps” and “dips” of the oscillation. The amplitude is responsible for the light intensity: the lower the oscillation, the weaker the light.
- Phase. This value, which is denoted as φ, we have already mentioned. Phase usually means the element of oscillation that occurs at a selected point in time. If we “caught” one wave at a maximum, the neighboring one on the rise, and the third at some point in the descent, then the phases of these oscillations do not coincide.
All wave properties, except, perhaps, the phase, are closely related to energy. The higher the frequency, the stronger the amplitude, the more energy the photon carries. Thus, the wavelength of monochromatic radiation also sets its “temperature” and place on the electromagnetic scale.
Scale of electromagnetic waves to the visible range
All types of light quanta are conditionally divided by wavelength. The boundaries between these zones are blurred, each section may consist of several more. Depending on the frequency, the electromagnetic scale contains:
- Radio and microwaves (3 kHz-300 GHz). They are divided into microwaves, centimeter, decimeter, meter, short, medium, long waves.
- Terahertz waves (300 GHz-3 THz).
- Infrared waves (150 GHz-405 THz). They are divided into near and far infrared ranges.
- Visible waves (405-790 THz). They are divided into seven colors: red, orange, yellow, green, blue, blue, purple.
The visible spectrum is so called precisely because the human eye is capable of perceiving it. Infrared light carries heat, and radio waves communicate.
Scale of electromagnetic waves after the visible range
But the radiation, which is located on the electromagnetic scale beyond the visible, is deadly for humans and other living beings:
- Ultraviolet waves (7.5 * 10 14 - 3 * 10 16 Hz). They are divided into near, middle, far, extreme (vacuum) spectra.
- X-ray waves (2 * 10 15 - 6 * 10 19 Hz). They are also called “X-rays”, since in English literature this section of the electromagnetic scale is simply referred to as “X-rays”. Subdivided into soft and hard spectra.
- Gamma radiation (coincides with the x-ray spectrum). The Greek letter designation “γ-radiation” may also occur. It differs from the X-ray spectrum by the method of preparation. Although gamma rays can have higher energies than x-rays.
Mankind has found application in these forms of light. Usually, when electromagnetic radiation is considered, the visible, IR and UV ranges are implied. But in fact, there is monochromatic light with a wavelength corresponding to x-rays and even gamma radiation. Just in artificial conditions, it is very difficult to obtain such synchronism for these waves.
Sources of electromagnetic radiation
The most common generators of electromagnetic radiation in the universe are stars. In their mighty bowels, the mass of incredibly compressed gas generates pure energy - quanta of light. The sun radiates in all spectra, but, fortunately, the Earth has an atmosphere. It protects all life from destructive waves with high and ultrahigh energy.
But do not think that only the Sun is accessible to humanity. The light of stars is also electromagnetic radiation. Sometimes the cosmos gives rise to gamma-ray bursts of such power that these photons rain down to the surface of our planet. Fortunately, the birth of supernovae takes place quite far from Earth. Otherwise, all living things to a depth of a kilometer from the surface would become sterile.
But people are cunning creatures. They penetrated the basis of the production of quanta and put them at their service. Some - on purpose, others - by accident. Mankind can receive radiation of any range: from gamma rays in atomic reactors to ultra-long waves for radio communications.
Monochromatic electromagnetic radiation
Now we come close to the main problem. So, if all the oscillations of the electromagnetic field from one source have the same wavelength, then this is a monochromatic wave. In the ideal case, the source of such light should be one allowed transition. But in practice, monochromatic light is a beam with a very narrow spread of wavelengths. In such cases, it is said that the wavelength of monochromatic light is equal to the most probable value of all received, that is, the most common photon in the beam. The source of such a stream of light is a laser. Not a single natural generator (for example, the Sun) is able to “force” its atoms to radiate equally.
The use of monochromatic light streams
The number of laser applications is innumerable. They came in handy everywhere.
Production, medicine, biology, geology, geography, archeology in the modern world would be different without lasers. But most often scientists use this device. The most interesting case is when a monochromatic wave is incident normally on the surface of the substance under study. In this case, transparent crystals reveal all their heterogeneities, and if a substance has some nonlinear properties, for example, it changes the refractive index of light, then the output is almost a work of art. A perpendicular beam of light will help determine the errors of opaque surfaces, the difference between lenses and spheres, or the level of light reflection.