l16 - Announcements Reminder: Schedule changes (see web...

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ISP209s10 Lecture 16 -1- Announcements Reminder: Schedule changes (see web page) No class on Thursday 3/18 Exam 2 pushed back to Tues. 3/30 You can bring 5 pages notes (front and back)! Review session on Thurs. 3/25 (lots of practice clicker questions, etc.) • Today: Quantum Mechanics (Ch.13/14) and start the Strong and Weak Forces
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ISP209s10 Lecture 16 -2- Why is Quantum Theory so strange? • What you thought were waves can act like particles and visa-versa (“wave-particle duality”) • Quantum uncertainty (Heisenberg) • Nature is intrinsically random • Quantum non-locality • Nature is “digital” and “discrete” • The very act of observing/measuring can change the outcome We don’t see any of the weirdness in our daily lives. But if you look at microscopically small phenomena (atoms), it seems to indeed be reality!
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ISP209s10 Lecture 16 -3- Sometimes light acts like a wave… Interference <=> waves Bright: Constructive interference Dark : Destructive interference
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ISP209s10 Lecture 16 -4- Look closer, you see light acts like a particle… E EM = 0, 1hf, 2hf, 3hf, 4hf, … h*f = energy of 1 photon EM fields are made of discrete bundles of energy (quanta or photons) h = 6.625E-34 Js Planck’s Constant Particle-like: We cannot predict the individual dots position. Quantum theory Can only predict the pattern that emerges with a large number of dots (probabilities).
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ISP209s10 Lecture 16 -5- Particles acting like waves Electrons show an interference pattern in the double slit experiment. And the interference Patterns show a Discrete “lumpiness” If you look closely. Each “lump” is an Electron hitting the Screen. As with light, it is impossible to predict the position Of each individual dot. Nature is intrinsically random! We can only predict “probabilities”, which is to say the overall pattern that emerges with a large # of dots. “electron gun”
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ISP209s10 Lecture 16 -6- Why don’t macroscopic objects give interference patterns Say you repeatedly throw baseballs at two macroscopic slits (e.g., the 2 class doors in the front of this room) The De Broglie wavelength Of a macroscopic object is So tiny that the “interference Fringes” are so close together That we don’t ever notice them.
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l16 - Announcements Reminder: Schedule changes (see web...

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