The highest peaks on a wave are called crests and the lowest peaks are called troughs. Wavelength is the distance between two adjacent crests or two adjacent troughs. For light, wavelengths determine color. The height of the wave is called amplitude. The amplitude of an electromagnetic wave shows its intensity. On Earth, we receive radiation from the sun as waves with high amplitude, making sunlight very bright. The waves from other stars have low amplitude when they reach the Earth, making their light less bright.
A third property of waves is frequency. Frequency is the number of wave units that repeat in a certain amount of time. The greater the frequency of the wave, the greater the energy it carries.
The full range of wavelengths and frequencies forms the electromagnetic spectrum, often abbreviated EM spectrum.
Electromagnetic waves are part of nature. They travel from the sun to Earth, acting to both warm and light the surface. Life on Earth would not be possible without the energy these waves bring! Many waves can be easily encoded to carry messages, and we see these applications in daily life. A radio receiver or a cell phone are examples. X-ray imaging is another example. Radio waves are typically used in wireless technology, which is communication without the use of wires, cables, or other physical media.
Infrared radiation also carries information in fiber optic cables. These cables carry pulses of infrared light, similar to pulses of electricity that are carried in ordinary phone wires.
X-rays and gamma rays from space are mostly deflected by Earth's atmosphere. Very little of this dangerous radiation reaches the surface. To study the universe with these types of rays, scientists have launched special telescopes into space.
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