Lect20 - Quantum Theory Chapter 28(1 of 2 Physics 104...

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11/15/11 1 Quantum Theory Particles and Waves Particle properties of light: Photons Wavelike properties of particles: electrons Electron spin Wavefunction Tunneling Physics 104, Fall 2011 1 Physics 104 Lecture 20 Nov. 14, 2011 Chapter 28 (1 of 2) 11/15/11 Quantum Mechanics! • At very small sizes the world is VERY different! – Energy is discrete, not continuous. – Probability of event to occur is calculable • Cannot guarantee outcome, a la, Newton’s laws. • Outcomes are not “deterministic” – Particles seem to be in two places at same time. – Looking at something changes how it behaves. • Perhaps, counterintuitive. – However, our intuition is based on our direct perception Physics 104, Fall 2011 2 11/15/11

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11/15/11 2 Blackbody Radiation First evidence for Q.M. Tuesday, November 15, 2011 Physics 104, Fall 2011 3 We know that hot objects emit light. This behavior could not be explained by classical wave theory. As the temperature increases Red hot Blue hot. Blue photons have higher energy than red photons. Example: Sunlight ~ 480nm Surface temperature of the sun is 6000K. Visible Light λ Max = 0.0029 K T m Max Blackbody Radiation First evidence for Q.M. Tuesday, November 15, 2011 Physics 104, Fall 2011 4 ! max Max Planck found he could explain these curves if he assumed energy of photon is quantized. E = hf Visible Light h = 6.626 X 10 -34 Joule sec Max Planck (1858-1947)
3 Work Function Energy is needed to release electrons from a metal. Each metal has a Work Function (W 0 ) which is also called Binding Energy (BE) . The work function, W c is the minimum energy required to remove a single electron from a piece of metal Photoelectric Effect Light shining on a metal can “knock” electrons out of atoms. Light must provide energy to overcome Coulomb attraction of electron to nucleus Light Intensity gives power/area If effect depends on power only: Amount of electrons released should increase linearly with intensity of light. Physics 104, Fall 2011

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Lect20 - Quantum Theory Chapter 28(1 of 2 Physics 104...

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