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# 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 b March 26, Saturday, LTJ s 2:30 to 5:00 pm b Covers Lectures 1 – 12 b Closed Book s Complicated formulae and physical constants will be provided s Fundamental Equations such as below will NOT be provided. b Lorentz Transform b E 2 = (pc) 2 + (mc 2 ) 2 , β ββ = pc/E s Key Discoveries leading to the new Quantum Mechanics You are expected to know: b How the experiment was done and what were the key observations b What the experiment proved, or disproved b In what ways are that experiment important You will not be tested on the date and the place of the experiments.
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 b From the Latin word quantus ‘how much’ b In physics, this means: s Can only exist in certain discrete amounts b Matter is quantized: atoms b Electric Charge is quantized: electron charge b Money is quantized: 10 cents in HK now b Students are quantized b Time is NOT quantized b Liquid Water is NOT quantized (until you get to the molecular level – but then it would not be liquid.) b Radiation (light) is WAVE! How can that be QUANTIZED ?
M.Loy Sp2010 5 Matter, Energy, Heat and Light b We long know matter, energy, heat and light are closely related. b Need fuel (wood or coal) to keep a fire burning, giving out heat. b When there is heat, there is light – and you can tell the temperature by the colour of the light. b 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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6 Electromagnetic Radiation b Both heat and light are electromagnetic radiation b Each kind of wave has its own frequency ν and wavelength λ . b Visible light has wavelengths between 400 nm and 700 nm, where the nanometer is 1 nm =10 -9 m. b EM wave, with wavelengths in the infrared, transmits the energy from a hot source to us as ‘heat’. b
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## This note was uploaded on 03/31/2011 for the course PHY 126 taught by Professor Hobunchan during the Spring '11 term at HKUST.

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

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