Physics » Electromagnetic Waves » The Electromagnetic Spectrum

# Summarizing the Electromagnetic Spectrum

## The Electromagnetic Spectrum Summary

• The relationship among the speed of propagation, wavelength, and frequency for any wave is given by $${v}_{\text{W}}=\mathrm{f\lambda }$$, so that for electromagnetic waves,

$$c=\mathrm{f\lambda },$$

where $$f$$ is the frequency, $$\lambda$$ is the wavelength, and $$c$$ is the speed of light.

• The electromagnetic spectrum is separated into many categories and subcategories, based on the frequency and wavelength, source, and uses of the electromagnetic waves.
• Any electromagnetic wave produced by currents in wires is classified as a radio wave, the lowest frequency electromagnetic waves. Radio waves are divided into many types, depending on their applications, ranging up to microwaves at their highest frequencies.
• Infrared radiation lies below visible light in frequency and is produced by thermal motion and the vibration and rotation of atoms and molecules. Infrared’s lower frequencies overlap with the highest-frequency microwaves.
• Visible light is largely produced by electronic transitions in atoms and molecules, and is defined as being detectable by the human eye. Its colors vary with frequency, from red at the lowest to violet at the highest.
• Ultraviolet radiation starts with frequencies just above violet in the visible range and is produced primarily by electronic transitions in atoms and molecules.
• X-rays are created in high-voltage discharges and by electron bombardment of metal targets. Their lowest frequencies overlap the ultraviolet range but extend to much higher values, overlapping at the high end with gamma rays.
• Gamma rays are nuclear in origin and are defined to include the highest-frequency electromagnetic radiation of any type.

## Glossary

### electromagnetic spectrum

the full range of wavelengths or frequencies of electromagnetic radiation

electromagnetic waves with wavelengths in the range from 1 mm to 100 km; they are produced by currents in wires and circuits and by astronomical phenomena

### microwaves

electromagnetic waves with wavelengths in the range from 1 mm to 1 m; they can be produced by currents in macroscopic circuits and devices

### thermal agitation

the thermal motion of atoms and molecules in any object at a temperature above absolute zero, which causes them to emit and absorb radiation

a common application of microwaves. Radar can determine the distance to objects as diverse as clouds and aircraft, as well as determine the speed of a car or the intensity of a rainstorm

a region of the electromagnetic spectrum with a frequency range that extends from just below the red region of the visible light spectrum up to the microwave region, or from $$0\text{.}\text{74}\phantom{\rule{0.25em}{0ex}}\mathrm{\mu m}$$ to $$\text{300}\phantom{\rule{0.25em}{0ex}}\mathrm{\mu m}$$

electromagnetic radiation in the range extending upward in frequency from violet light and overlapping with the lowest X-ray frequencies, with wavelengths from 400 nm down to about 10 nm

### visible light

the narrow segment of the electromagnetic spectrum to which the normal human eye responds

### amplitude modulation (AM)

a method for placing information on electromagnetic waves by modulating the amplitude of a carrier wave with an audio signal, resulting in a wave with constant frequency but varying amplitude

### extremely low frequency (ELF)

electromagnetic radiation with wavelengths usually in the range of 0 to 300 Hz, but also about 1kHz

### carrier wave

an electromagnetic wave that carries a signal by modulation of its amplitude or frequency

### frequency modulation (FM)

a method of placing information on electromagnetic waves by modulating the frequency of a carrier wave with an audio signal, producing a wave of constant amplitude but varying frequency

### TV

video and audio signals broadcast on electromagnetic waves

### very high frequency (VHF)

TV channels utilizing frequencies in the two ranges of 54 to 88 MHz and 174 to 222 MHz

### ultra-high frequency (UHF)

TV channels in an even higher frequency range than VHF, of 470 to 1000 MHz

### X-ray

invisible, penetrating form of very high frequency electromagnetic radiation, overlapping both the ultraviolet range and the $$\gamma$$-ray range

### gamma ray

($$\gamma$$ ray); extremely high frequency electromagnetic radiation emitted by the nucleus of an atom, either from natural nuclear decay or induced nuclear processes in nuclear reactors and weapons. The lower end of the $$\gamma$$-ray frequency range overlaps the upper end of the X-ray range, but $$\gamma$$ rays can have the highest frequency of any electromagnetic radiation

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