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# Electromagnetic radiation

Electromagnetism |
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Electricity · Magnetism |

Lorentz force law • emf • Electromagnetic induction • Faraday’s law • Lenz's law • Displacement current • Maxwell's equations • EM field •
Electromagnetic radiation • Liénard–Wiechert potential • Maxwell tensor • Eddy current |

**Electromagnetic waves** are waves that contain an electric field and a magnetic field and carry energy. They travel at the speed of light.^{[1]}

Quantum mechanics developed from the study of electromagnetic waves. This field includes the study of both visible and invisible light. Visible light is the light one can see with normal eyesight in the colours of the rainbow. Invisible light is light one can't see with normal eyesight and includes more energetic and higher frequency waves, such as ultraviolet, x-rays and gamma rays. Waves with longer lengths, such as infrared, micro and radio waves, are also explored in the field of Quantum mechanics.

Some types of electromagnetic radiation, such as X-rays, are ionizing radiation and can be harmful to your body. Ultraviolet rays are near the violet end of the light spectrum and infrared are near the red end. Infrared rays are heat rays and ultraviolet rays cause sunburn.

The various parts of the electromagnetic spectrum differ in wavelength, frequency and quantum energy.

Sound waves are not electromagnetic waves but waves of pressure in air, water or any other substance.

## Mathematical formulation

In physics, it is well known that the **wave equation** for a typical wave is

[math]\nabla ^2 f=\frac{1}{c^2}\frac{\partial^2 f}{\partial t^2}[/math]

The problem now is to prove that Maxwell's equations explicitly prove that the electric and magnetic fields create electromagnetic radiation. Recall that two of Maxwell's equations are given by

[math]\nabla \times \mathbf{E}=-\frac{\partial \mathbf{B}}{\partial t}[/math]

[math]\nabla \times \mathbf{B}=\mu_o \mathbf{j}+\mu_o \epsilon_o \frac{\partial \mathbf{E}}{\partial t}[/math]

By evaluating the curl of the above equations and vector calculus one can prove the following equations

[math]\nabla ^2 \mathbf{E}=\frac{1}{c^2}\frac{\partial^2 \mathbf{E}}{\partial t}[/math]

[math]\nabla^2 \mathbf {B}=\frac{1}{c^2}\frac{\partial^2 \mathbf{B}}{\partial t}[/math]

Note: the proof involves making the substitution

[math]c=\frac{1}{\sqrt {\mu_o \epsilon}}[/math]

The equations above are analogous to the wave equation, by replacing **f** with **E** and **B**. The above equations mean that propagations through the magnetic (**B**) and electric (**E**) fields will produce waves.

## Related pages

## References

- Hecht, Eugene (2001).
*Optics*(4th ed. ed.). Pearson Education.

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- Serway, Raymond A.; Jewett, John W. (2004).
*Physics for Scientists and Engineers*(6th ed. ed.). Brooks/Cole.

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- Tipler, Paul (2004).
*Physics for Scientists and Engineers: Electricity, Magnetism, Light, and Elementary Modern Physics*(5th ed. ed.). W. H. Freeman.

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- Reitz, John; Milford, Frederick and Christy, Robert (1992).
*Foundations of Electromagnetic Theory*(4th ed. ed.). Addison Wesley.

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- Jackson, John David (1975).
*Classical Electrodynamics*(2nd ed ed.). John Wiley & Sons.

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- Allen Taflove and Susan C. Hagness (2005).
*Computational Electrodynamics: The Finite-Difference Time-Domain Method, 3rd ed.*. Artech House Publishers.

. http://www.artechhouse.com/default.asp?Frame=Book.asp&Book=1-58053-832-0&Country=US&Continent=NO&State=.

## Other websites

*Electromagnetic Waves from Maxwell's Equations*on Project PHYSNET.- Conversion of frequency to wavelength and back - electromagnetic, radio and sound waves
- eBooks on Electromagnetic radiation and RF
- The Science of Spectroscopy - supported by NASA. Spectroscopy education wiki and films - introduction to light, its uses in NASA, space science, astronomy, medicine & health, environmental research, and consumer products.