Types Of Electromagnetic Radiation

The electromagnetic spectrum is usually divided into several different regions according to wavelength, with the most common classification scheme including radio waves, microwaves, terahertz radiation, infrared radiation, visible light, ultraviolet light, X-rays, and gamma rays.

Radio waves have wavelengths from one millimeter to hundreds of meters and frequencies of about 3 Hz to 300 GHz. They are commonly used to transmit data for television, mobile phones, wireless Internet connections, and many other applications.

Wavelength (crest to crest)

High energy Short wavelength

Wavelength (crest to crest)

Low energy Long wavelength

Gamma

X-rays

Ultraviolet

Infrared

Microwave

FM

TV

Short

AM

rays

rays

rays

wave

10-6 10"2 1 102 104 — — ^ Wavelength (meters)

Visible light

Visible light

500 600

Wavelength (nanometers)

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The electromagnetic spectrum

The complex technology to encode radio waves with data involves changing the amplitude and frequency and phase relations of waves within a specific frequency band.

Microwave radiation wavelengths range from one millimeter to one meter and frequencies between 0.3 GHz and 300 GHz. It includes super-high-frequency (SHF) and extremely-high-frequency classes. Microwaves are absorbed by molecules with dipolar covalent bonds, a property used to heat material uniformly, and in rapid amounts of time, in microwave ovens.

Terahertz radiation wavelengths range between the far infrared and microwaves, and frequencies between 300 GHz and 3 terahertz. Radiation in this region can be used for imaging and communications and in electronic warfare to disable electronic equipment.

Infrared radiation has wavelengths between visible light and terahertz radiation, and frequencies of 300 GHz (1 mm) to 400 Terra Hertz (750 nm). Far-infrared radiation (300 GHz to 30 THz) is absorbed by the rotation of many gas molecules, by the molecular motions in liquids, and by phonons (a quantized mode of vibration of a crystal lattice) in solid phases. Most of the far-infrared radiation that enters the Earth's atmosphere is absorbed except for a few wavelength ranges (called windows) where some energy can penetrate. Mid-infrared radiation has frequencies from 30 to 120 THz, and includes thermal radiation from black bodies (i.e., bodies that absorb all energy at all wavelengths when they are cold). Near-infrared radiation is similar to visible light and has frequencies from 120 to 400 THz.

Higher-frequency radiation (400-790 THz) with wavelengths between 400 and 700 nanometers is detectable by the human eye and is known as visible light. It is also the range of most of the radiation emitted from the Sun and stars. When objects reflect or emit light in the visible range, the human eye and brain process data from these wavelengths into an optical image of the object. The details of how the human brain perceives radiation from these wavelengths and processes it into an image is not completely understood and is actively studied by many molecular biologists, neuroscientists, psychologists, and biophysicists.

Ultraviolet radiation has wavelengths shorter than visible light and longer than X-rays, falling between 400 and 10 nm, and has energies between 3 and 124 electron volts. Ultraviolet radiation is emitted by the sun and is a highly energetic ionizing radiation that can induce chemical reactions, may cause some substances to glow or fluoresce, and can cause sunburn on human skin. The ultraviolet radiation from the sun is poisonous to most living organisms but is

CHARACTERISTICS OF ELECTROMAGNETIC RADiATiON

Class

Frequency

Wavelength

Energy

Gamma rays

300 EHz

1 pm

1.24 MeV

Hard X-rays

30 EHz

10 pm

124 keV

3 EHz

100 pm

12.4 keV

Soft X-rays

300 PHz

1 nm

1.24 keV

30 PHz

10 nm

124 eV

Extreme ultraviolet

3 PHz

100 nm

12.4 eV

Near ultraviolet

300 THz

1 pm

1.24 eV

Near Infrared

30 THz

10 pm

124 meV

Mid-Infrared

3 THz

100 pm

12.4 meV

Far Infrared

300 GHz

1 mm

1.24 meV

Extremely high frequency

30 GHz

10 mm (1 cm)

124 peV

Super high frequency

3 GHz

100 mm (1 dm)

12.4 peV

Ultra high frequency

300 MHz

1 m

1.24 peV

Very high frequency

30 MHz

10 m

124 neV

High frequency

3 MHz

100 m

12.4 neV

Medium frequency

300 kHz

1 km

1.24 neV

Low frequency

30 kHz

10 km

124 peV

Very low frequency

3 kHz

100 km

12.4 peV

Voice frequency

300 Hz

1 Mm

1.24 peV

Super low frequency

30 Hz

10 Mm

124 feV

Extremely low frequency

3 Hz

100 Mm

12.4 feV

absorbed by the atmospheric ozone layer, preventing significant damage to life on Earth.

X-rays have wavelengths from 10 to 0.01 nanometers with frequencies from 30 petahertz to 30 exahertz (30 x 1015 Hz to 30 x 1018 Hz) and energies from 120 eV to 120 keV. X-rays can "see" through some objects (like flesh) but not others (like bones) and can be used to produce images for diagnostic radiography and crystallography. In the cosmos X-rays are emitted by neutron stars, some nebulae, and the accretion disks around black holes.

Gamma rays are the most energetic photons and have no lower limit to their wavelength. Their frequency is greater than 1019 Hz, their energies are more than 100 keV, and their wavelengths are fewer than 10 picometers. Gamma rays are highly energetic and ionizing, so they can cause serious damage to human tissue and are a serious health hazard.

See also astronomy; astrophysics; Coriolis effect; cosmic microwave background radiation; interstellar medium; origin and evolution of the universe; remote sensing.

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