Electromagnetic Waves
Maxwell's equations predict self-sustaining waves of electric and magnetic fields that propagate at the speed of light and span the electromagnetic spectrum.
Definition
Electromagnetic waves are coupled oscillations of electric and magnetic fields, transverse and in phase in vacuum, that satisfy the wave equation derived from Maxwell's equations and carry energy and momentum at the speed of light through space or media.
Scope
This area covers the wave solutions of Maxwell's equations: plane and other electromagnetic waves in vacuum and in media, polarization, energy and momentum transport by waves, reflection and refraction at interfaces, dispersion and absorption, and guided propagation in waveguides and transmission lines. It treats the full electromagnetic spectrum as a single phenomenon, while the emission of radiation by sources is handled in the radiation-and-antennas area.
Sub-topics
Core questions
- How do Maxwell's equations give rise to propagating waves?
- How are waves polarized and how do they transport energy?
- How do waves behave at boundaries and in dispersive media?
- How are electromagnetic waves guided in structures?
Key concepts
- wave equation
- plane wave
- polarization
- electromagnetic spectrum
- phase and group velocity
- reflection and refraction
- dispersion
- waveguide
Key theories
- Electromagnetic wave equation
- Combining Maxwell's curl equations yields a wave equation for the fields with propagation speed set by the electric and magnetic constants, equal to the speed of light and identifying light as an electromagnetic wave.
- Transverse, polarized plane waves
- In free space the electric and magnetic fields of a plane wave are mutually perpendicular and perpendicular to the direction of propagation, with the orientation of the electric field defining the polarization.
- Existence of electromagnetic waves (Hertz)
- Hertz generated and detected electromagnetic waves in the laboratory, confirming Maxwell's prediction and demonstrating reflection, refraction, and polarization analogous to light.
Clinical relevance
Electromagnetic waves underpin radio and wireless communication, radar, fiber-optic and free-space optics, microwave and millimetre-wave systems, and imaging across the spectrum from radio to X-rays in medicine and industry.
History
Maxwell predicted electromagnetic waves in the 1860s and identified light as one such wave. Hertz confirmed their existence experimentally in 1887-1888, and the rapid development of radio by Marconi and others, together with the optics tradition of Fresnel, established the unity of the electromagnetic spectrum.
Key figures
- James Clerk Maxwell
- Heinrich Hertz
- Augustin-Jean Fresnel
Related topics
Seminal works
- jackson1998
- born1999
- hertz1893
Frequently asked questions
- Why do electromagnetic waves travel at the speed of light?
- The wave equation from Maxwell's equations has a propagation speed fixed by the permittivity and permeability of the medium; in vacuum this speed equals the measured speed of light, showing light is an electromagnetic wave.
- Are radio waves and visible light the same kind of thing?
- Yes; they are all electromagnetic waves differing only in frequency and wavelength, together forming the electromagnetic spectrum from radio waves through microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.