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Photon energy

The energy of a photon is usually found with the formula which uses Planck’s contant:

Where:

  • is the energy of the photon (in joules)
  • is Planck’s constant, which is approximately joule-seconds
  • is the frequency of the photon (in hertz)

Remember, this finds the energy of a single photon. If you have a beam of light, you would need to multiply this by the number of photons in the beam to find the total energy.

Finding from wavelength

Section titled “Finding from wavelength”

We know that we can find the frequency using , from our topic on wave speed. Since the speed of light is constant, , we can use that to find the energy of a photon from its wavelength:

Where:

  • is the energy of the photon (in joules)
  • is Planck’s constant, which is approximately joule-seconds
  • is the speed of light (approximately meters per second)
  • is the wavelength of the photon (in meters)