Lesson Plan: Photon Momentum Physics • 9th Grade

This lesson plan includes the objectives, prerequisites, and exclusions of the lesson teaching students how to calculate the momentum of a photon given its frequency or wavelength.


Students will be able to

  • recognize that photons have momentum, even though they do not have mass,
  • recognize that, for one photon, this momentum is very small,
  • recognize that the momentum of a photon is inversely proportional to its wavelength,
  • recognize that the momentum of a photon is directly proportional to its frequency,
  • use the formula 𝑝=𝜆,
  • use the formula 𝑝=𝑓𝑐,
  • find the total momentum of 𝑛 identical photons, given the wavelength or frequency of each photon.


Students should already be familiar with

  • the idea that light can be modeled as a wave,
  • terms for the basic properties of waves: frequency, period, wavelength, wave speed, and amplitude,
  • how to use the formula 𝑣=𝑓𝜆,
  • the idea that light travels at a speed 𝑐 in a vacuum, with a value approximately equal to 3.00×10 m/s,
  • how to represent numbers using scientific notation,
  • the idea that light consists of particles called photons.


Students will not cover

  • compton scattering,
  • the de Broglie wavelength of massive particles,
  • radiation pressure.

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