When talking about electromagnetic fields, it is unavoidable to use technical and physics terms. To make it easier for the reader, a few general terms are explained here.
Current intensity
Electric field
Electromagnetic field
Electromagnetic spectrum
Electromagnetic wave
Extremely low frequencies (ELF)
Fields
Frequency
Infrared light (IR)
Intermediate frequencies (IF)
Ionising radiation
Magnetic field
Microwaves
Non-ionising radiation
Optical radiation
Phase
Photons
Power
Radio frequencies (RF)
Rays
Three-phase voltage
Ultraviolet light (UV or UV radiation)
Voltage
Wavelength
Current intensity
The quantity of electric charges that are generated per time unit. Is measured in ampere (A).
Electric field, E
Electric charges generate an electric field. An electric field is present around every wall socket. The intensity of it decreases quickly as the distance to the source increases. The higher the voltage in the cables, the larger the electric field is. The electric field is measured in volt per metre (V/m).
Electromagnetic spectrum
Radio waves, infrared light, visible light, ultraviolet light, x-rays, gamma rays, etc. are all electromagnetic waves. They only differ in frequency from one another: the faster the waves follow one another, the higher the frequency. The frequency determines the type, the specific characteristics and the application of electromagnetic waves. Our body reacts differently to waves of varying frequencies. The entirety of electromagnetic waves is called the electromagnetic spectrum. The spectrum contains both ionising and non-ionising radiation depending on the frequency and the photon energy.
Fig 3
Source : FPS Economy
Electromagnetic wave, electromagnetic field
The electric field and the magnetic field are considered separately when the frequencies are very low (for example 50 Hz). When the frequencies are high, the electric field and the magnetic field are indivisible and are marked as an electromagnetic wave or electromagnetic field in their entirety. In an electromagnetic wave, the electrical and magnetic components propagate perpendicular to each other in space.
Fig 2
Up
Extremely low frequencies (ELF)
That is how frequencies are called between 0 Hz and 300 Hz. Sources in our environment include high-voltage lines and other electrical supplies, electrical equipment, electrically driven vehicles, etc.
Frequency
The frequency of an electromagnetic wave is the number of wave peaks that passes by a certain point per second. One cycle per second is one hertz (Hz). The derived units of kilohertz (1 kHz = 1,000 hertz), megahertz (1 MHz = 1 million hertz), gigahertz (1 GHz = 1 billion hertz) are used for high frequencies.
Infrared light (IR)
Infrared light (IR) is invisible optical radiation with a wavelength that is longer than visible light. Infrared light is found just under red light in the electromagnetic spectrum. Hence, the name infrared. Depending on the wavelength, 3 types are differentiated: IRA, IRB and IRC, or near-infrared, mid-infrared and far-infrared. We cannot see infrared light but we can feel it as warmth on our skin. Despite the fact that we cannot see IR, it can be harmful for our eyes.
Intermediate frequencies (IF)
These are frequencies between 300 Hz and 100 kHz. Among others, antitheft and identification systems are sources of these.
Ionising radiation
High-energy photons are able to take away electrons from atoms and molecules they encounter. As a result, the atoms and molecules are charged electrically: this is called ionisation. Ionising radiation includes x-rays, gamma rays and part of the ultraviolet rays. (see also the electromagnetic spectrum)
Magnetic field, B or H
When electric current flows through wires, in other words, when electricity is consumed (for instance when a bulb is on or a vacuum cleaner is running), the electric charges move and generate a magnetic field around the wires and the device (this phenomenon is called induction). The intensity of the field decreases quickly as the distance to the source increases. The intensity of the magnetic field depends on the current intensity. The magnetic field is measured in Tesla (T) but the magnetic fields in our environment are usually so small that they are expressed in microtesla (1 microtesla = 1 millionth of a Tesla, 1 µT = 0.000001 T).
Non-ionising radiation
Electromagnetic waves, whereby the energy of the photons is not high enough to cause ionisation, fall under non-ionising radiation. The ultraviolet light with smaller frequency, visible light, infrared rays, radio waves and electromagnetic fields of intermediate and extremely low frequencies (IF- and ELF fields) are non-ionising. The electromagnetic rays that originate from artificial sources - electricity, microwave ovens, mobile telephones - are in that part of the spectrum. (see also the electromagnetic spectrum)
Optical radiation
Optical radiation is not only visible light but also UV light and infrared light. Despite the fact that we cannot see UV and IR, it can be harmful to our eyes when the exposure is too intense or lasts too long. In addition, optical radiation can also be harmful to the skin.
Phase
The phase expresses how much slower a wave is, compared to another wave. The phase is expressed in degrees or wavelengths (1 wavelength = 360°). The phase difference is equal to 0 when two waves run parallel. The waves are then in phase. If this is not the case, the waves are out of phase. They are in antiphase when two waves have a phase difference that is equal to half of the wavelength (in other words, 180°). Two waves in antiphase cancel out one another.
Fig 4 Waves with the same phase
Fig 5 Waves with a different phase
Photons
An electromagnetic wave transports energy in small packages, called photons. The higher the frequency, the higher the photon energy.
Power
The power depends on both the voltage and the current and reflects the energy consumption per time unit. The power is measured in watt (W). That is why we refer to wattage of a device. In practice, we sometimes use milliwatt as a unit (1 milliwatt = 1 thousandth of a watt, 1 mW = 0.001 W).
Radio frequencies (RF) and microwaves
Radio waves have a frequency between 100 kHz and 300 GHz. Microwaves also belong to the radio waves. Radio waves are used for radio broadcasting, TV, radar for aviation, speed control on the road by means of radar, mobile telephony, etc.
Rays/fields
The word rays is used most of the time for high frequencies: in this case, there is a transfer of energy (energy flow) in space. The emission of energy is negligible for low frequencies. That is why we refer to this as fields even though this word is sometimes used for high frequencies.
Three-phase voltage
A generator in an electric power plant contains three separate windings that have shifted spatially 120° compared to one another. Because the generator continually turns past these windings, and passes them one by one, the generated voltages are not at their maximums at the same time; the three voltages are 120° out of phase. That is why it is called three-phase voltage.
Fig 1.
Ultraviolet light (UV or UV radiation)
UV light is invisible optical radiation with a shorter wavelength than visible light. Ultraviolet light is found just next to violet light in the electromagnetic spectrum. Hence, the name ultraviolet. Depending on the wavelength, 3 types of UV radiation are differentiated: UVA, UVB and UVC. UVA has the longest wavelength and UVC has the shortest one. The shorter the wavelength, the higher the energy of the radiation and the more harmful it can be to the skin and eyes. In other words, UVB is more harmful than UVA. UVC is even more harmful than UVB but is fortunately blocked by the atmosphere.
Voltage
This is the potential difference between two points or the effort that is required to bring an electric charge from one point to the other. The voltage is measured in volt (V). That is why the voltage is sometimes also called the electrical potential. For high-voltage one uses kilovolt (1 kV = 1,000 volt).
Wavelength
The distance between two wave peaks is the wavelength (expressed in metre, millimetre, micrometre, etc.). The higher the frequency, the smaller the wavelength.