35_compton - Lesson 35: Compton Effect The photoelectric...

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Lesson 35: Compton Effect The photoelectric effect and Einstein's theories about light having a particle nature caused a lot of scientists to start to reexamine some basic ideas, as well as come up with some new ones. Based on a lot of Einstein's work (including his Special Theory of Relativity), physicists predicted that these photons should have momentum, just like other particles do. The tough part is explaining and proving this in a reasonable way, since you don't exactly feel light hammering you into the floor. The momentum that the light photons have must be very small, and not based on the common way of calculating momentum using p = mv (since light has no rest mass). Instead the formula was based on the wavelength and frequency of the light, just like Planck's formula. p = h or p = hf c p = momentum (kgm/s) h = Planck's Constant (always 6.63e-34) λ = wavelength (m) f = frequency (Hz) c = speed of light In 1923 A.H. Compton started shooting high frequency x-rays at various materials and found that his results seemed to support the idea of photons having momentum. In one setup he shot the high frequency x-rays at a piece of graphite . If light was a wave, we would expect the x-rays to come out the other side with their wavelength smaller ( Illustration 1 ). Basically we can explain this as the waves squishing when they hit the graphite, like a ball squishing when it hits the ground. 5/5/2010 © studyphysics.ca Page 1 of 4 / Section 14.3 Do you find it kind of odd that we're talking about all this stuff supporting the theory that light acts like a particle, and yet still doing calculations using values for wavelength and frequency? Sounds kinda wave-like to me. I don't blame you. This is
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This note was uploaded on 12/02/2011 for the course PHYSICS 235 taught by Professor Staff during the Fall '08 term at Rutgers.

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35_compton - Lesson 35: Compton Effect The photoelectric...

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