Wavicles It has previously been shown to follow directly from Maxwell’s equations that for an electromagnetic wave of constant average intensity, the photonic pressure P in empty space is given by P = P / A c , where P is the power in the wave, A is the area, and c is the speed of light. Pressure, however, is force over area, so A can be cancelled in each denominator to give F = P /c . Finally, constant force is momentum p per unit time just as constant power is energy U per unit time, so after another pair of cancellations, it is found that an electromagnetic wave can be considered to have a momentum p = U/c . Since it has already been established that the energy in a single photon is U = hf , this would seem to indicate that the massless “ wavicle ” called a photon has a momentum p = h/ λ . Of course, reality is not required to obey results derived mathematically, but in 1922, a experimental physicist named Compton discovered an effect supporting this idea. He
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