Lectures on Physics has been derived from Benjamin Crowell's Light and Matter series of free introductory textbooks on physics. See the editorial for more information.... 
Home Modern Physics Light as a Particle Examples Momentum of a photon  
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Momentum of a photonAccording to the theory of relativity, the momentum of a beam of light is given by p = E/c (see homework problem 10 on page 39). Apply this to find the momentum of a single photon in terms of its frequency, and in terms of its wavelength. Combining the equations p = E/c and E = hf , we find
To reexpress this in terms of wavelength, we use c = fλ:
The second form turns out to be simpler.


Home Modern Physics Light as a Particle Examples Momentum of a photon 