These are the waves that do not need a material medium to propagate, unlike other types of waves, such as sound. James Clerk Maxwell, the Scottish physicist, was the first to make the theoretical observation that a variable electromagnetic field admits a solution whose equation of motion corresponds to that of a wave, hence electromagnetic waves. This suggested that the electromagnetic field was capable of propagating in the form of waves, both in a material medium and in a vacuum.
In his theory of relativity, Albert Einstein came up with the theoretical solution that explains the constancy of the speed of light, which since the 17th General Conference on Weights and Measures in 1983 it was agreed to set 299,792,458 m / sec. However, usually it is said that it is 300,000 km/sec. These waves make up electromagnetic radiation; it is a combination of oscillating electric and magnetic fields, which propagate through space transporting energy from one place to another.
Parts of an Electromagnetic Wave
Wavelength: Distance between two ridges.
- Amplitude: It is the maximum disturbance of the wave—half the distance between the ridge and the valley.
- Frequency: Number of times the wave repeats per unit of time. If Hertz is used, it is the number of times the wave repeats for each second.
There are also two other interesting facts:
- Period: 1 / frequency. It is the inverse of the frequency.
- Speed: the speed of the wave depends on the medium through which it propagates (where it travels).
Electromagnetic waves are three-dimensional (by their number of directions of propagation) and transversal. The main idea is that if electric charges are made to oscillate between the ends of an antenna, an electric field and a magnetic field are generated, interacting with each other. Electromagnetic waves are the result of the interaction of these two fields.
How Do We Differentiate Them?
We use frequency to recognize them (remember the number of times the wave is repeated). The higher a frequency is, the shorter its wavelength. They can be ordered in a spectrum that ranges from very high-frequency waves (small wavelengths) to very low frequencies (high wavelengths). The electromagnetic spectrum is composed of gamma rays, X-rays, ultraviolet radiation, visible light, infrared rays, microwaves, and radio waves.
- Gamma Rays – They are produced by subatomic processes such as the annihilation of a positron-electron pair or by radioactive elements. They are also generated in astrophysical phenomena of great violence. Gamma radiation is composed of photons; they are produced by nuclear or subatomic transitions, and usually, the frequency of this radiation is greater than 1020 Hz, so it has an energy greater than 100 keV and a wavelength less than 3×10-13 m, much less than the diameter of an atom. Due to their high energies, gamma rays can cause severe damage to the nucleus of cells, which is why they are used to sterilize medical equipment and food.
- X-Rays – Arise from extra-nuclear phenomena, at the level of the electronic orbit, mainly produced by the deceleration of electrons. X-rays are ionizing radiation because when interacting with matter, it causes ionization of its atoms; that is, it creates charged particles. They are invisible to the human eye, capable of passing through opaque bodies and printing photographic films. X-rays penetrating power: They pass through matter. The penetration capacity increases as the kilovoltage goes higher; the lower the density of the matter, the lower the average atomic number of a said matter passed through. Current digital systems allow obtaining and viewing the radiographic image directly on a computer without the need to print it. The wavelength is between 10 to 0.01 nanometers, which corresponds to frequencies within the range of 30 to 30,000 PHz.
- Ultraviolet Radiation – Its wavelength is approximately between 10 nm (10×10−9 m) and 400 nm (400×10−9 m). The name derives from the fact that its range begins from wavelengths shorter than what the human eye identifies as violet. Ultraviolet light is not visible to the human eye because it is above the visible spectrum. This radiation is an integral part of the sun’s rays and produces various health effects as it is between non-ionizing and ionizing radiation.
- Visible Light – There are no exact limits to the visible spectrum: the typical human eye will respond to wavelengths from 380 to 750 nm, although in rare cases, some people may be able to see light with wavelengths from 310 to 1050 nm.
- Infrared Rays – This radiation has a longer wavelength than visible light but shorter than microwaves. Therefore, it has a frequency that is lower than visible light and higher than microwaves. Its wavelengths range from about 0.7 to 1000 micrometers. Infrared radiation is emitted by any object whose temperature is greater than 0 Kelvin, that is, −273.15 degrees Celsius (absolute zero).
- Microwaves – Generally between 300 MHz and 30 GHz, which assumes an oscillation period of 3 s (3 × 10−9 s) to 33 s (33 × 10−12 s) and a wavelength in the range of 10 mm at 1 m. One of the most famous applications of microwaves is microwave ovens, which use a magnetron to produce waves at a frequency of approximately 2.45 GHz. These waves cause water molecules to vibrate or rotate, which generates heat. Since most foods contain a significant percentage of water, they can be easily cooked this way. In telecommunications, microwaves are used in broadcasting, as they pass easily through the atmosphere with less interference than other longer wavelengths.
- Radio Waves – They propagate from frequencies of 10 THz to 10 kHz, whose corresponding wavelengths are from 100 micrometers (0.0039 inches) to 100 kilometers (62 miles). Radio waves can be created by natural processes such as lightning or by astronomical phenomena. They can also be artificially generated and are used mainly for communications.