Electromagnetic Wave

Author: Rino , Created on Jul 30, 2025 2 min read

Energy that propagates through space as waves composed of oscillating electric and magnetic fields, fundamental to light and all wireless communication.

physics electromagnetism

Electromagnetic Wave

What is an Electromagnetic Wave?

An Electromagnetic (EM) wave is energy that propagates through space in the form of waves composed of in-phase, oscillating electric and magnetic fields that are perpendicular to each other. It does not require a medium and can travel through a vacuum at the speed of light, c.

James Clerk Maxwell (Scottish, 1831-1879) proposed Maxwell's equations, which describe electromagnetic phenomena, in the 1860s and predicted the existence of EM waves.

Maxwell's Equations (In-depth)

Maxwell's equations consist of four differential equations that form the core of classical electromagnetism. They elegantly unify electricity and magnetism and reveal the nature of light as an electromagnetic wave.

  1. Gauss's law for electricity: Describes how electric charges produce electric fields.
  2. Gauss's law for magnetism: States that there are no magnetic monopoles.
  3. Faraday's law of induction: Describes how a changing magnetic field creates an electric field.
  4. Ampère's circuital law with Maxwell's addition: Describes how an electric current or a changing electric field creates a magnetic field.

The Electromagnetic Spectrum

EM waves can be arranged into a continuous spectrum based on their frequency (or wavelength):

(Low Frequency / Long Wavelength) <— — — — — — — (High Frequency / Short Wavelength) Radio - Microwave - Infrared - Visible - UV - X-ray - Gamma ray

  • Radio Waves are the basis for all wireless communication, from Amateur Radio used by hobbyists to mobile phone communication.
  • Visible Light is just a very narrow band of the entire electromagnetic spectrum that the human eye can perceive.

Properties

  • Exhibit Wave–particle duality, showing properties of both waves (interference, diffraction) and particles (photoelectric effect).
  • Energy is proportional to frequency (E = h\nu). Higher-frequency EM waves, like X-rays, carry more energy.
  • Popular Science:
    • (Book) QED: The Strange Theory of Light and Matter by Richard P. Feynman.
  • Textbooks:
    • (Book) Fundamentals of Physics by David Halliday, Robert Resnick, Jearl Walker.
  • Further Reading:
    • (Book) Introduction to Electrodynamics by David J. Griffiths.