lecture8 - Physics 126 Lecture 8 March 3 2011 Energy...

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M.Loy, H. B. Chan 1 Physics 126 Lecture 8 March 3, 2011 Energy Quantum and the Hypothesis for the Light Quantum Suggested Reading: Chapter 2.1 to 2.4 Waves Optical Spectra Black Body Thermal Radiation Stephan-Boltzmann Law Wien Displacement Law Planck’s Energy Quanta: Planck’s Radiation Theory Einstein’s Light Quanta Hypothesis: Photoelectric Effect Theory Millikan’s Photoelectric Effect Experiment
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M.Loy, H. B. Chan 2 Midterm exam box4 March 26, Saturday, LTJ square6 2:30 to 5:00 pm box4 Covers Lectures 1 – 12 box4 Closed Book square6 Complicated formulae and physical constants will be provided square6 Fundamental Equations such as below will NOT be provided. box4 Lorentz Transform box4 E 2 = (pc) 2 + (mc 2 ) 2 , β β = pc/E square6 Key Discoveries leading to the new Quantum Mechanics You are expected to know: box4 How the experiment was done and what were the key observations box4 What the experiment proved, or disproved box4 In what ways are that experiment important You will not be tested on the date and the place of the experiments.
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M.Loy, H. B. Chan 3 Quantization: Matter vs. Light What is Matter? Electrons, X-Ray, Radioactivity, atomic nature of matter, atomic nucleus ( Quantization of Matter) (Lec 7) What is radiation (including light, infra red heat wave, etc)? • Blackbody radiation (equilibrium between radiation and matter) spectrum • Photoelectric effect Both inconsistent with the classical theory of electromagnetism and statistical physics. Energy is ‘quantized’ Quantization of Light .
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M.Loy Sp2010 4 Quantization box4 From the Latin word quantus ‘how much’ box4 In physics, this means: square6 Can only exist in certain discrete amounts box4 Matter is quantized: atoms box4 Electric Charge is quantized: electron charge box4 Money is quantized: 10 cents in HK now box4 Students are quantized box4 Time is NOT quantized box4 Liquid Water is NOT quantized (until you get to the molecular level – but then it would not be liquid.) box4 Radiation (light) is WAVE! How can that be QUANTIZED ?
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M.Loy Sp2010 5 Matter, Energy, Heat and Light box4 We long know matter, energy, heat and light are closely related. box4 Need fuel (wood or coal) to keep a fire burning, giving out heat. box4 When there is heat, there is light – and you can tell the temperature by the colour of the light. box4 The heat energy is radiated to you via infrared radiation : you do not have to touch the fire to be warmed. Everyone can see the connection between heat and light!
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M.Loy Sp2010 6 Electromagnetic Radiation box4 Both heat and light are electromagnetic radiation box4 Each kind of wave has its own frequency ν and wavelength λ . box4 Visible light has wavelengths between 400 nm and 700 nm, where the nanometer is 1 nm =10 -9 m. box4 EM wave, with wavelengths in the infrared, transmits the energy from a hot source to us as ‘heat’.
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