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Unformatted text preview: PHYS142/143 Rm 4.110 Ph. 02 42214798 Email: carey_freeth@uow.edu.au Wave Particle Duality of Light As we have seen, electromagnetic radiation has two aspects, a wave aspect and a particle aspect. Interference and diffraction of e.m. radiation are explained by assuming e.m. radiation consists of waves. Quantum effects, such as the photoelectric and Compton effect are explained by assuming e.m. radiation consists of particle like photons, each photon with energy E and momentum p speciFed precisely by the frequency, ! , and wavelength, " , of the radiation. ! = E h " = h p (Maxwell predicted e.m. waves also has linear momentum, and that Each equation contains both a wave concept ( ! and " ) and a particle concept (E and p). i.e. Travels as a wave and exchanges energy & momentum as a particle. Note: Any energytransport phenomenon must be described in terms of waves or of particles, but we cannot simultaneously apply a particle description and a wave description. As we have seen, we only need to use one or other description when considering the properties of light  we can't and never need to use both to explain the same experiment. p = E c = h ! c = h " . ) De Broglie Waves De Broglie suggested in 1924 that since light has a dual waveparticle nature then matter may also have this duality. In analogy with e.m. radiation, de Broglie postulated that the wavelength of a matter wave associated with a particle whose momentum is p would be where m is the relativistic mass of the particle. Note: for an objects " to be large enough to produce observable wave effects, its mass and velocity must be small [see equation], and low speed non relativistic relations may often be used. Because the wave nature of Xrays was veriFed (in 1912) from diffraction experiments using the atoms of a crystal as an array of diffracting centres, it was quickly recognised that the wave nature of matter could be tested in the same way. Laue Xray diffraction pattern for quartz crystal. e.g. since the typical distance between adjacent atoms is of the order of 0.100 nm, to observe diffraction the electrons wavelength must be comparable and so the K.E. of the electron must be: K.E. = 1 2 m e v 2 = p 2 2m e = 1 2m e h !...
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This note was uploaded on 08/20/2010 for the course PHYS 142 taught by Professor Xxx during the One '09 term at University of Wollongong, Australia.
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