Electromagnetic radiation
What we mean by the term electromagnetic radiation is the release of electromagnetic energy in space in the form of waves, which are called electromagnetic waves. Electromagnetic waves are simultaneously oscillating electric and magnetic fields that are produced in planes perpendicular to each other and perpendicular to the propagation direction of the electromagnetic wave.
These waves propagate in space with a speed equal to the speed of light (c = 299,792,458 m/s) and also in matter with a speed slightly lower than the speed of light.
Historical data
James Clerk Maxwell (June 13, 1831 – November 5, 1879), the greatest theoretical physicist of the 19th century, by combining the known theories of electricity and magnetism at the time, proposed a single theory called “Theory of Electromagnetism”, which was able to solve all known problems. Explain that time in this field of physics. But the value of his theory was not limited to the interpretation of phenomena that were known until then. He predicted the existence of electromagnetic waves even before they were discovered.
Electromagnetic waves were first produced and detected by Hertz in 1887, eight years after Maxwell’s death. In the early 19th century, researchers discovered that electricity and magnetism are related phenomena. In 1865, Maxwell formulated four equations, which are known today as Maxwell’s equations, taking into account all the previous experiences of researchers (Coulomb, Ampere, Faraday). These equations describe all electromagnetic phenomena. The importance of these equations in electromagnetism is equivalent to the importance of Newton’s laws in mechanics.
Maxwell's equations
Maxwell did not formulate all these equations himself, but he expressed them in general, pointed out their importance and through them predicted the existence of electromagnetic waves that propagate at the speed of light.
The first is Gauss’s law: electric charges produce an electric field. The electric current on the closed surface is proportional to the enclosed charge.
The second is Gauss’ law of magnetism: there are no magnetic monopoles. The magnetic flux in a closed surface is zero.
The third is Faraday’s law of induction: time-varying magnetic fields produce an electric field.
The fourth equation is Ampere’s law modified by Maxwell. Maxwell’s correction states that the source of the magnetic field is not only the electric current but also the changing electric field. It is worth noting that at that time no experiment had been done to prove that a changing electric field could create a magnetic field. By examining the last two equations of Maxwell, we see that electromagnetic waves are created in the following conditions:
Changing magnetic fields that themselves create electric fields.
Changing electric fields that themselves create magnetic fields.
The electromagnetic theory formulated by Maxwell relates electric and magnetic fields to their sources. The source of the electric field is not only charges, but also changing magnetic fields, and on the other hand, the source of the magnetic field is not only currents, but also changing electric fields. According to this theory, the change of one field implies the creation of another field.
According to Maxwell, such changes in electric and magnetic fields, such as sound waves or water waves, must propagate through space at the speed of light. A few years later, Hertz experimentally confirmed Maxwell’s predictions by generating electromagnetic waves in the laboratory and measuring their speed. The electromagnetic theory formulated by Maxwell played an important role in the formulation of Einstein’s theory of relativity. With the theory of relativity, many fundamental concepts of physics were revised, but Maxwell’s equations remained intact.
Wave properties of electromagnetic radiation
As previously mentioned, electromagnetic radiation can be described by electric and magnetic fields that are in phase and in the form of sinusoidal oscillations perpendicular to each other and in the direction of radiation propagation.
Many properties of electromagnetic radiation are easily described by the classical sinusoidal model, where parameters such as wavelength, frequency, speed, and intensity are used.
Electromagnetic radiation, unlike other wave phenomena such as sound, does not need a material environment to propagate, but is also transmitted in a vacuum.
Electromagnetic radiation wave parameters
Amplitude or A in a sine wave is the length of the electric vector at the maximum wave.
Wavelength or λ is the linear distance between two equivalent points in continuous waves.
Period or P is the time between two peaks or two valleys in seconds.
Frequency or v is the number of field oscillations per second (seconds or Hertz). The frequency of the radiation beam is determined by the source and remains unchanged. On the other hand, the wavelength of the radiation depends on the composition of the material in which the radiation is emitted.
The energy of electromagnetic waves
Therefore, the electromagnetic wave carries energy. This energy, which is transferred at the speed of light, can be related to the energy of photons, which also move at the speed of light. According to postclassical theories, light has wave-particle properties. This means that it can be thought of as waves or particles. which are equivalent to each other.
Electromagnetic waves are often referred to as radiation. This term includes both the wave property (radius) and the particle property (shot). The electromagnetic wave proves all the phenomena of reflection, absorption, refraction and diffraction. If we consider that the small particles that enter the radiation become emitters of secondary radiation in all directions, all these mentioned cases will be easily interpreted.
Emission of electromagnetic radiation
Electromagnetic radiation is emitted when excited particles return to lower energy levels by releasing their excess energy as photons. Stimulation can be done in the following ways:
Bombardment with electrons or other elementary particles (produces X-rays)
Exposure to spark, flame, arc or furnace heat (ultraviolet, visible, infrared)
Radiation with electromagnetic radiation (fluorescence phenomenon)
exothermic chemical reaction (chemiluminescence phenomenon)
Spectrum of electromagnetic radiation
Often we hear a lot about electromagnetic fields, electromagnetic waves, electromagnetic radiation. These are basically all the same thing that we see from different points of view. If we look at them from a structural point of view, i.e. field, if we look at them from the point of view of how they propagate, we use the term waves, and if we examine them from the point of view of energy, we use the term radiation.
There are infinite sources of electromagnetic radiation in nature and in everyday life. The Earth’s electromagnetic field, magnets, hundreds of household appliances including radios, televisions, computers, sunlight, and lasers are all sources of electromagnetic radiation.
The world is scattered by electromagnetic radiation. The light emitted by the stars is part of the total spectrum of electromagnetic radiation in the universe. Electromagnetic radiation has a very wide spectrum and its frequency varies from several hundred Hz to 1022 Hz.
Since frequency and wavelength are related by the simple relationship E=f.λ, we sometimes use wavelength instead of frequency to specify a wave. Electromagnetic radiation is divided into the following sections depending on the frequency of the waves and the transmitting energy.
It is worth noting that all forms of electromagnetic radiation move at the speed of light and are even able to penetrate certain materials.
Radio waves
Radio waves are electromagnetic waves with a relatively low frequency. They cover the frequency range of 0-300 MHz. The energy of their photons is very low and reaches up to 6-10 electron volts. These waves are produced by antennas and can be widely used in telecommunications. These waves are divided into subcategories based on their frequency or wavelength. The lowest bandwidth of radio waves is the industrial wave area and the highest bandwidth is the ultra short wave area.
Microwave waves
Microwave waves are also considered a part of radio waves because they are produced by antennas and have many applications in telecommunications. However, due to the higher energy of their photons, they have different properties than other radio waves. Microwave waves cover the frequency between 300 MHz and 300 GHz, and their photon energy is between 10-6 and 10-3 EV. Ten waves are also divided into three sub-regions. UHF decimeter microwave band, SHF centimeter microwave band and EHF millimeter microwave band.
Infrared waves
Infrared radiation covers a frequency band between 300 GHz and 400 Hz, and the energy of its photons is from 10-3 to 1.6 electron volts. All objects emit infrared radiation when heated. These radiations have many technological applications. Infrared radiation is used in optical electronic media such as CD players, in electronic communications with optical fibers, and also with wireless infrared transmission. Infrared photography, which is used in archeology, agriculture, ecology, forestry, geology and hydrology, is also one of the very important applications of these waves.
Visible light waves
The visible light region is a narrow band of the electromagnetic radiation spectrum that the human eye is sensitive to. These waves cover the frequency range of 400 to 800 Hz and the energy of its photons is between 1.6 and 3.2 electron volts. The visible spectrum is divided into regions that the human eye perceives as different colors.
Ultraviolet waves
Ultraviolet radiation covers the frequency range of 800 to 1017 x 3 Hz, and the energy of the photons of these waves is between 3 and 2000 electron volts, which are emitted by very hot objects such as stars. Ultraviolet radiation is an energetic radiation and is completely harmful to living tissues.
x-ray
X-rays cover the frequency range of 1019 x 5 to 1017 x 3 Hz and photon energy of 1200 to 105 x 2.4 rel electron volts. The most common way to produce X-rays is by accelerating electrons through a potential difference of tens of thousands of volts and hitting them on a target made of metallic materials with a large atomic number.
Gamma waves
Gamma radiation is a very high frequency radiation that covers the frequency range of 5×019 to 3×1022 Hz. The energy of its photons is very high and varies from 105 to 107 electron volts. Gamma rays are produced by radioactive nuclei and stars in space.
Ionizing and non-ionizing radiation
The electromagnetic spectrum is also divided into two sub-regions: ionizing and non-ionizing rays.
Ionizing electromagnetic radiation has a higher frequency than visible light, is shorter in wavelength, and carries much higher energy. Ionizing radiations include ultraviolet light from the sun, cosmic rays, X-rays and gamma rays of radioactivity. This form of radiation is dangerous because it can cause ionization (the breaking down of DNA strands in cells that causes cancer and other diseases). Non-ionizing electromagnetic radiation has a frequency lower than or equal to that of visible light, has a long wavelength and carries relatively little energy, which is not enough to cause ionization, that is, to break chemical bonds in cell molecules. As a result, they do not pose health risks like ionizing radiation. This category includes radiation emitted from radio transmitters, mobile phone antennas, radar, electrical and electronic devices.
More information about frequencies
The electromagnetic spectrum, or (EM), is a term used to describe the many different energy fluctuations that make up our known universe. These oscillations range from the slow motion of low-energy electrons to the faster motion of higher-energy photons of visible light and other waves. We can consider the different energy regions of the electromagnetic spectrum as unrelated phenomena because our senses perceive them differently.
We see visible light as color, feel infrared as heat, and so on. But all these energies are connected sequentially as a sequence of waves in the electromagnetic spectrum. The nature of particles depends on the speed of their movement and the characteristics they manifest. Most of the frequencies of the electromagnetic spectrum are perceived by humans through their effects.
We understand and differentiate between the waves of the electromagnetic spectrum depending on the natural way they manifest. For example, we have access to the radio spectrum frequencies that transmit and receive these waves with an antenna. An x-ray machine uses special radiation in the x-ray range that allows us to see inside the body and more.
As we explained earlier, the existence of an electromagnetic field is a combination of an electric field and a magnetic field. All energies in the electromagnetic spectrum have different frequencies. The term frequency refers to the number of cycles per second during which a wave travels and is measured in Hertz. Waves also have different sizes or lengths that are distinguished by terms such as microns, angstroms, nanometers.
By increasing the number of waves in a given space (in other words, their frequency) per second, their size becomes smaller. And by decreasing the number of waves per second, their size will be bigger. In other words, the higher the frequency or oscillation rate of a wave, the shorter the wavelength of that wave. The lower the frequency or rate of oscillation of a wave, the longer the wavelength of that wave.
Electromagnetic radiation (EM) and electromagnetic fields (EMF) work somewhat differently. Both emanate from an electromagnetic source. But the energy of radiated waves is independent of its source. It is removed from its source and continues to exist even when the source is inactive. But on the other hand, when the power supply is deactivated, the electromagnetic fields will no longer exist.
Static electricity and magnetism are both static fields that have a complex and intimate relationship with each other. An oscillating electric field creates an oscillating magnetic field and an oscillating magnetic field creates an oscillating electric field. Each is at a right angle to the other. Importantly, when motion is observed in a stationary electric field or in a magnetic field, they become electromagnetic fields.
The performance of different bioelectromagnetic devices is based on this. The spectrum of electromagnetic waves is often compared to sound, because the two phenomena are similar in many ways. Sound consists of mechanical pressure waves and is created when an object moves with enough force to move (compress) the surrounding air or other conductors capable of transmitting these waves.
We hear many of these waves (airflow) as acoustic frequencies (sound) because when air reaches the ear, it moves the eardrum and sends the oscillations to the brain, where it is converted into movement sound, music, speech, and so on. etc. is decoded.
The term wave frequency, which is used to describe the spectrum of electromagnetic waves, also applies to music, which is part of sound. The pitch of a note depends on its frequency. Low frequency produces low sound. A higher frequency produces a higher pitch.
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