Electromagnetic wave

All forms of light within the electromagnetic spectrum can be thought of as electromagnetic waves produced by the interplay of their electric and magnetic fields.

Illustrations of electromagnetic waves
  • Electromagnetic waves can be visualized as synchronized oscillations of electric and magnetic fields that propagate at the speed of light in a vacuum.
  • Illustrations of electromagnetic waves may highlight:
    • Velocity (v): Measures the rate and direction a wave moves in a specific medium.
      • Velocity represents the speed and direction at which an electromagnetic wave propagates through a medium. It is typically constant for a given medium and is unrelated to wavelength, frequency, or amplitude.
    • Wavelength (λ): The distance over which the shape of a wave repeats. Wavelength is measured in meters or sub-units of metres.
      • wavelength is inversely related to frequency (), according to the equation . This means that as the wavelength increases, the frequency decreases, and vice versa.
    • Frequency (f): Frequency is measured in cycles per second. The unit of frequency is Hertz.
    • Amplitude (A): Amplitude is the maximum magnitude of the wave’s oscillations. It represents the peak value of the wave’s electric and magnetic fields as they oscillate in space.
      • Amplitude is not directly related to velocity, wavelength, or frequency mathematically. However, amplitude does affect the energy carried by the wave. In some contexts, amplitude may be related to the intensity or power of the wave.


Electromagnetic waves consist of coupled oscillating electric and magnetic fields orientated at 900 to one another. (Credit: https://creativecommons.org/licenses/by-sa/4.0)

About the properties of photons
  • A photon is a type of elementary particle that is a quantum (plural = quanta) of the electromagnetic field. This means that it is the smallest quantity into which light can be divided.
  • A photon carries energy and can be described both in terms of a particle and a wave.
  • While the wave model of light works well for some phenomena, the particle model is necessary to explain others.
  • Light can exhibit both wave-like and particle-like behaviour depending on the experiment performed. This is known as wave-particle duality.
  • The wavelength of a photon determines its energy and frequency.
  • Photons with longer wavelengths have lower energy and frequency, while photons with shorter wavelengths have higher energy and frequency.
  • The wavelength of a photon can also affect its behaviour, such as its ability to penetrate materials or cause photochemical reactions.

Other properties of photons include:

  • Photons have zero rest mass but have energy and momentum proportional to their frequency.
  • Unlike other kinds of elementary particles, photons have no rest mass.
  • Photons are electrically neutral, meaning they have no electric charge.
  • Photons are stable particles that do not decay over time.
  • Photons can interact with other particles, such as electrons, through processes such as absorption and emission.
  • Photons can interact with other particles, such as electrons, through processes like absorption and emission.
  • Photons always travel at the speed of light in a vacuum, regardless of their frequency or energy.

An electromagnetic wave carries electromagnetic radiation.

  • An electromagnetic wave is formed as electromagnetic radiation propagates from a light source, travels through space and encounters different materials.
  • Electromagnetic waves can be imagined as synchronised oscillations of electric and magnetic fields that propagate at the speed of light in a vacuum.
  • Electromagnetic waves are similar to other types of waves in so far as they can be measured in terms of wavelength, frequency and amplitude.
  • We can feel electromagnetic waves release their energy when sunlight warms our skin.
  • Remember that electromagnetic radiation can be described either as an oscillating wave or as a stream of particles, called photons, which also travel in a wave-like pattern.
  • The notion of waves is often used to describe phenomena such as refraction or reflection whilst the particle analogy is used when dealing with phenomena such as diffraction and interference.