* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Modern Physics Lesson 3
Atomic orbital wikipedia , lookup
Renormalization group wikipedia , lookup
Quantum key distribution wikipedia , lookup
Bremsstrahlung wikipedia , lookup
Hydrogen atom wikipedia , lookup
Electron configuration wikipedia , lookup
Relativistic quantum mechanics wikipedia , lookup
X-ray photoelectron spectroscopy wikipedia , lookup
Quantum electrodynamics wikipedia , lookup
Arthur Compton wikipedia , lookup
Rutherford backscattering spectrometry wikipedia , lookup
Renormalization wikipedia , lookup
Elementary particle wikipedia , lookup
Ultrafast laser spectroscopy wikipedia , lookup
Wheeler's delayed choice experiment wikipedia , lookup
Bohr–Einstein debates wikipedia , lookup
Particle in a box wikipedia , lookup
Delayed choice quantum eraser wikipedia , lookup
Double-slit experiment wikipedia , lookup
Atomic theory wikipedia , lookup
Matter wave wikipedia , lookup
X-ray fluorescence wikipedia , lookup
Wave–particle duality wikipedia , lookup
Theoretical and experimental justification for the Schrödinger equation wikipedia , lookup
Modern Physics Lesson 3. The Compton Effect and Photon Momentum Blue Book § 27-4, 5, 6 The photoelectric effect showed that a photon, or quantum of light, behaves like a particle, since it has kinetic energy (even though it has no mass). This was a VERY BIG DEAL since light had always been thought of as a wave before. Einstein proposed that photons should also have momentum, and then showed that this momentum would equal: p h hf (since c f ) c Note also that E hf hc pc (for a photon) This theory was tested in 1922 by A.H. Compton. He directed X-rays (which have short wavelength, therefore high energy) at a graphite target. The rays were scattered by the atoms in the graphite. Compton measured that the scattered X-rays had a longer wavelength, which means they had lost some energy and momentum in the scattering process. Unscattered rays (λ) graphite X-ray spectrometer Scattered rays (λ’) X-ray source What happened to the “lost” energy and momentum? Compton looked and looked for it, and found electrons being emitted from the graphite. He tested them and found that they had the same amount of energy that had been lost by the photons in the X-rays. It was as though the photon and electron had had an elastic collision (like billiard balls). This was more evidence for the Quantum Theory. Energy and momentum were conserved by the photons!! Conclusion: A photon is a particle of light that has energy and momentum. However, photons have no mass and travel at the speed of light, c. deBroglie Wavelength Louis deBroglie proposed in 1923 that if waves behave like particles, then particles should also behave like waves! This was the beginning of the idea of WAVE-PARTICLE DUALITY, the concept that everything has both wave and particle properties. deBroglie’s calculation of the wavelength of any particle went like this: p h h p or h mv This can obviously only be used for objects with mass (i.e., NOT photons). It is usually used for electrons and protons, since they are the only objects that display noticeable wave-like properties. Normal sized objects (like a book or a basketball) also have a deBroglie wavelength, but it is so small that you could never notice it. Experiments have backed up deBroglie’s idea – electrons and protons have been shown to display diffraction patterns, a property that only waves have. Example. Calculate the deBroglie wavelength of (a) a 1.0 kg basketball traveling at 0.50 m/s, and (b) an electron traveling at 150 m/s. (1.3 × 10-33 m, 4.8 × 10-6 m) HW. Blue Book p. 853 Q13, 16, P27, 36 (3.2 × 10-32 m), 37