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- Electromagnetic waves
- The electromagnetic spectrum
Test prep for ap courses
The correct ordering from least to greatest wavelength is:
- ELF, FM radio, microwaves, infrared, red, green, ultraviolet, x-ray, gamma ray
- ELF, FM radio, microwaves, infrared, green, red, ultraviolet, x-ray, gamma ray
- gamma ray, x-ray, ultraviolet, red, green, infrared, microwaves, FM radio, ELF
- gamma ray, x-ray, ultraviolet, green, red, infrared, microwaves, FM radio, ELF
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Section summary
- The relationship among the speed of propagation, wavelength, and frequency for any wave is given by
, so that for electromagnetic waves,
where
is the frequency,
is the wavelength, and
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.
Conceptual questions
If you live in a region that has a particular TV station, you can sometimes pick up some of its audio portion on your FM radio receiver. Explain how this is possible. Does it imply that TV audio is broadcast as FM?
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Illustrate that the size of details of an object that can be detected with electromagnetic waves is related to their wavelength, by comparing details observable with two different types (for example, radar and visible light or infrared and X-rays).
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Source:
OpenStax, College physics for ap® courses. OpenStax CNX. Nov 04, 2016 Download for free at https://legacy.cnx.org/content/col11844/1.14
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