Radio waves are a form of electromagnetic radiation used for communication, radar, and astronomy. They are produced by the movement of electric charge and can be encoded using amplitude or frequency modulation. Radio waves have a broad range of wavelengths and frequencies, making them useful for long-distance communication. Concerns have been raised about the health effects of exposure to radio waves, particularly those in the microwave range, but clinical studies have been inconclusive. Radio waves were first predicted by James Clerk Maxwell in 1865 and were experimentally demonstrated by Heinrich Hertz in 1887.
Radio waves are an invisible form of electromagnetic radiation (EMR) that range in wavelength from approximately 0.04 inch (one millimeter) to over 62,000 miles (100,000 km), making it one of the broadest ranges on the electromagnetic spectrum. “Radio” is a generic term describing all forms of EMR with a wavelength greater than 0.04 inch (one millimeter) and a frequency less than 300 GHz. It is generated by the movement of electric charge, which can result from a current electricity or by the random movement of atoms and molecules. This form of EMR is critical to human communications and is used for television, radio, and cell phones, as well as radar and astronomy.
How are radio waves produced?
All electromagnetic radiation can be thought of as waves rippling through an electromagnetic field, like ripples in a pond. They are produced when an electrically charged particle, usually an electron, changes its speed or direction of motion. This can occur in various ways, such as heating of atoms and molecules and changes in the energy levels of electrons; the waves generated by radio transmitters result from the flow of electric current. The frequency and wavelength depend on the amount of energy involved, with higher frequencies and shorter wavelengths indicating higher energies. If the energy change is relatively small, radio waves can be produced.
it is used
The best known use of radio waves is to send images, audio and text in the form of signals: the long wavelength of radio allows it to go around obstacles and travel long distances, unlike visible light and other radiations to higher frequency. Radio waves with a wavelength of less than about 10 meters are absorbed by the atmosphere. The longer waves bounce back and forth between the ionosphere and the ground, making radio ideal for broadcasting over the horizon. The lower frequencies are used for communication with submarines, due to their low energy – for stealth – and high penetrating power. These lower frequencies can be thought of as having more “bass,” meaning they penetrate further, especially through dense media such as water.
To send information over radio waves, it must be encoded in some way. There are two main methods, known as amplitude modulation (AM) and frequency modulation (FM). In AM, information is encoded by varying the amplitude, or height, of waves, while the FM method involves using changes in frequency to carry data. Patterns of different amplitudes or frequencies are decoded where they are received to reproduce the original information, which can be images, sounds or text. In this way, complex information can be transmitted over long distances at low cost.
Radio astronomy is a fundamental tool for understanding the universe. Due to the existence of gas and dust clouds in galaxies, there is a limit to the amount of information that can be obtained using visible light or higher EMR frequencies. Radio waves, however, can pass through these obstacles, and much of what has been learned about the interiors of galaxies has come from analyzing natural radio sources. Astronomers were also able to detect the radiation from the big bang itself, which, due to the expansion of the universe, was extended from its initial very high frequencies into the microwave range – this is known as the cosmic microwave background ( CMB ).
Health effects
Concerns have been expressed about the possible health effects of exposure to radio waves, particularly those in the microwave range, used by cell phones and radars. When radiofrequency radiation is absorbed by tissue, it can cause warming. Normal exposure is not believed to cause any problems, but being in close proximity to a powerful radar transmitter can be potentially dangerous. The lens of the eye is particularly susceptible to damage from heating, and excessive exposure to microwave radiation could potentially lead to cataracts. There is also concern about the long-term effects of frequent cell phone use, but as of 2013, clinical studies have been inconclusive.
History
Radio waves were first predicted in 1865 by James Clerk Maxwell, who invented the equations for electromagnetism, later known as Maxwell’s equations. As he worked on the relationship between electromagnetism and light, he realized that other forms of electromagnetic radiation were possible, with wavelengths above and below the visible range. The existence of lower wavelength radiation was experimentally demonstrated 22 years later, in 1887, when Heinrich Hertz generated radio waves in his laboratory. Within a few decades, they were widely used for information transmission. Guglielmo Marconi and Nikola Tesla are both credited with being early pioneers in the field of radio, but Marconi patented the first wireless telegraphy system in 1896.
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