Electromagnetic Waves

They sound high-tech, but they're all around you, and they've helped shape communications for almost an entire century.

Radio
Television
Satellites

How Things Work: Radio
How Things Work: Television
Answers to common questions by University of Virginia Physics Professor Lous A. Bloomfield.

Electromagnetic waves are created when a moving electric charge creates a changing electric field. This induces a changing magnetic field to travel directly opposite the electric field. Continuously, another electric field is created, and a perpendicular magnetic field is created to counter it. The fields pull each other along, constituting an electromagnetic wave. The electric and magnetic fields can vary in strength along the wave.

The entire group of these waves is called the electromagnetic spectrum. There are many different ranges of frequency. Frequency is the number of cycles the wave completes in a second. Short frequency waves are measured by an angstrom or Å, which is equivalent to the diameter of one hydrogen atom. Longer wave measurements are expressed in hertz (cycles per second) or Hz. This measurement was named after German Heinrich Hertz, a radio pioneer. The highest frequency rays known are cosmic rays, and are 10 000 000 000 000 000 (ten thousand trillion) times larger than the shortest waves. Higher frequency waves have more energy but shorter wavelengths.

Radio waves measure between a few kilohertz (1000 Hz) and several gigahertz (1 billion Hz). In a vacuum all electromagnetic waves travel at about 300 000 km per second (about 186 000 miles per second).

Radio waves are used in broadcasting radio and television stations, wireless telephone transmission, radar, navigational systems and space communications. On earth, changes such as air pressure variations can reduce the velocity of transmissions. This, as well as other storm and electrical disturbances can cause anomalies in the propagation of the waves. Earth’s spherical form makes long-distance radio communication possible. Waves within a certain frequency can be reflected in the atmosphere’s ionosphere, travelling across the earth, allowing anyone receive the transmission.

Sources
Click here for a list of sources used in this project.
Glossary
All the words in bold are found in the Glossary. If you don't understand a word, click on the beside it, to go directly to the Glossary Page.
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