MS. Ankita P. Angre Dept. of Physics Dnynasadhana college, Thane Class-F. Y. B. Sc. Subjet-Physics Paper-II SEMESTER II Topic: Compton Effect MS. Ankita P. Angre Dept. of Physics

Compton Effect Einstein said light consists of quanta of energy (1905) He did NOT treat momentum until later (1906) He said momentum = E/c = hf/c Debye and Compton treated photon-particle collisions much later (1923)

X-Rays Discovered in 1895 by Roentgen High speed electrons onto a metal target and get a new highly penetrating radiation Medical X-Rays came within months EM waves with very short wavelengths (very high frequency) Wavelengths of about 10-10 meters, same spacing as atoms in crystals

Spectrum of X-Rays Broad continuous spectrum Characteristic lines from different elements Bremsstrahlung (braking radiation) eV=hf=hc/min min=hc/eV where V is tube voltage Already evidence of particle nature of x-rays

X-Ray Scatting from Crystals Atoms in successive planes scatter constructively if path difference is a whole number of wavelengths, n=2dsin n=1,2,3…. d  A C   B

Compton Effect Considered X-rays scattering from free electrons Classically, should get re-radiation at equal or lower frequencies Classically, re-radiated frequency depends on intensity and exposure time Experimentally, frequency shift is independent of time and intensity

Compton Effect Wavelength shift depends only on scattering angle Consider a collision between a photon and a free electron Photon energy is hf and momentum is hf/c Do a relatavistic calculation

Compton Effect Ee. pe Photon, E, p   E’<E,p’

Compton Effect

Compton Effect Eliminate  and solve for pe

Compton Effect So, shift only depends on angle and gives a result that agrees with experiment

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