The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. It provides a way of categorizing the vast array of electromagnetic waves that occur in the universe, from the lowest frequencies used for radio communication to the highest frequencies that ionize atoms. Understanding the electromagnetic spectrum is crucial for numerous technological advancements and provides the foundation for fields such as radio technology, medicine, astronomy, and even our understanding of the fundamental nature of the universe.
What Is the Electromagnetic Spectrum?
The electromagnetic spectrum is the continuous spectrum of electromagnetic radiation. It covers an enormous frequency range, from about 1 hertz (Hz) at the extreme low end to over 1025 Hz at the high end, with no gaps in the frequency range.
Electromagnetic radiation refers to the waves of the electromagnetic field, propagating through space and carrying electromagnetic radiant energy. It includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. Electromagnetic radiation exhibits both wave-like and particle-like behavior. Parameters such as frequency and wavelength describe its wave-like behavior. But, it is also a stream of photons, with each photon carrying a discrete amount of energy proportional to its frequency.
Classes of Electromagnetic Radiation
Here are the main classes of electromagnetic radiation, listed from lowest to highest frequency:
- Radio Waves
- Microwaves
- Infrared Radiation
- Visible Light
- Ultraviolet Radiation
- X-rays
- Gamma Rays
The part of the electromagnetic spectrum with the longest wavelength and lowest frequency is radio. The portion with the shortest wavelength and highest frequency is gamma radiation. Visible light, which is the portion of the spectrum that we can see, is roughly in the middle. It has a shorter higher frequency than infrared, but lower frequency than ultraviolet.
Electromagnetic Spectrum Table
Here is a summary of the frequencies, wavelengths, and example uses of different parts of the electromagnetic spectrum:
| Region | Frequency Range | Approximate Wavelength | Example Uses |
|---|---|---|---|
| Radio Waves | 101−109 Hz | >1m | Broadcasting, communications |
| Microwaves | 109−1012 Hz | 1mm−1m | Cooking, radar, communications |
| Infrared | 1012−1014 Hz | 700nm−1mm | Thermal imaging, remote control |
| Visible Light | 1014−1015 Hz | 400−700nm | Human vision, photography |
| Ultraviolet | 1015−1017 Hz | 10−400nm | Sterilization, tanning |
| X-rays | 1017−1019 Hz | 0.01−10nm | Medical imaging, security scans |
| Gamma Rays | >1019 Hz | <0.01nm | Radiation therapy, astronomy |
Describing Electromagnetic Waves
Scientists describe electromagnetic waves using three primary properties: frequency (f), wavelength (λ), and photon energy (E). These properties relate to one another through the following formulas:
- c=f×λ
Where c is the speed of light in a vacuum (3×108 m/s) - E=h×f
Where h is Planck’s constant (6.62607015×10−34 m2kg/s)
Photon energy and wavelength are related by substituting the frequency in terms of the speed of light and wavelength into the second formula:
- E=λhc
Atmospheric Penetration of the Electromagnetic Spectrum
Not all classes of electromagnetic radiation penetrate the Earth’s atmosphere:
- Radio Waves and Microwaves: Largely penetrate the atmosphere, which is why ground-based radio telescopes are effective.
- Infrared Radiation: Partially absorbed; specialized telescopes at high altitudes or in space are used for infrared astronomy.
- Visible Light: Mostly penetrates the atmosphere, which is why most optical telescopes are ground-based.
- Ultraviolet, X-rays, Gamma Rays: Largely absorbed by the atmosphere; telescopes for these bands are in space.
For this reason, many specialized telescopes and other observational instruments are placed on satellites orbiting outside Earth’s atmosphere.
Ionizing vs. Non-Ionizing Radiation
The electromagnetic spectrum includes both ionizing and non-ionizing radiation.
- Non-Ionizing Radiation: Radio waves, microwaves, infrared, visible light and some ultraviolet light are forms of non-ionizing radiation. They have lower energy and do not have enough energy to remove tightly bound electrons from atoms.
- Ionizing Radiation: Short-wavelength ultraviolet, X-rays, and gamma rays are ionizing radiation. They have enough energy to remove tightly bound electrons, which can damage or kill living cells and pose a radiation risk.
References
- Browne, Michael (2013). Physics for Engineering and Science (2nd ed.). New York: McGraw Hill/Schaum. ISBN 978-0-07-161399-6.
- Feynman, Richard; Leighton, Robert; Sands, Matthew (1963). The Feynman Lectures on Physics, Vol. 1. USA: Addison-Wesley. ISBN 978-0-201-02116-5.
- Grupen, Claus; Cowan, G.; Eidelman, S. D.; Stroh, T. (2005). Astroparticle Physics. Springer. ISBN 978-3-540-25312-9.
- L’Annunziata, Michael; Baradei, Mohammad (2003). Handbook of Radioactivity Analysis. Academic Press. ISBN 978-0-12-436603-9.
- Mohr, Peter J.; Taylor, Barry N.; Newell, David B. (2008). “CODATA Recommended Values of the Fundamental Physical Constants: 2006”. Reviews of Modern Physics. 80 (2): 633–730. doi:10.1103/RevModPhys.80.633