Introduction to Modern Physics

Introduction to Modern Physics - Midterm Exam Exam will be...

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1 Midterm Exam ± Exam will be Saturday, 26 March, 2011, LTJ, 2:30 to 5:00 pm ± Arrive early. Seats will be assigned. Check before you enter. ± The exam will cover up to and including Lecture 12. ± Physical constants will be provided. ± Bring your own calculator
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2 Physical Constants & Conversion Factors will be provided.
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3 The following formulae are provided.
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4 How about the rest? Should I memorize them all? ± The most important thing is to UNDERSTAND the concepts. ± Why I provide Compton Scattering but not, for example, photoelectric effect ? ± Reason: The entire conceptual physical content of PE effect is in that simple equation. The important points are simply that light behaves as energy quanta of h ν and can cause electrons to be ejected with energy ( h ν – work function). If you understand the effect, you would for sure remember the equation. ± On the other hand, the important conceptual physical content of Compton scattering is NOT only that equation – that equation is the result of the calculation. ± What are the important points in Compton Scattering?
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5 Some Important Points of Compton Scattering ± Treat photon as particle with energy h ν and momentum h/ λ ± Using relativistic mechanics conservation laws, the Compton scattering formula can be derived. (You should do it so you understand how!) ± You should memorize those conservations laws: » Conservation of relativistic energy » Conservation of relativistic momentum In summary, know the starting point and know how the end result can be derived, rather than just memorizing the formulae. For the more complicated formulae (Planck radiation, Compton scattering, etc), I will provide them.
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6 Einstein’s Theory of Relativity (1905) Two postulates (assumed to be true): (1) Principle of Relativity: Physical laws can be applied in all inertial frames : the same laws of electrodynamics and optics will be valid for all frames of reference for which the equations of mechanics hold good.” (2) Velocity of light is constant: ”light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body “These two postulates suffice for the attainment of a simple and consistent theory of the electrodynamics of moving bodies based on Maxwell's theory for stationary bodies .”
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7 Newton: Time is independent of motion Distance Velocity Stationary {s} Observer d s =V y t s Vy Moving {m} Observer d m =(d s 2 + x 2 ) ½ V m = (V x 2 + V y 2 ) 1/2 Tm = Ts t d 0 t X = V x t m u t T s The distance traveled as observed in {m} is larger than the distance traveled as observed in {s}. The velocity in {m} is correspondingly larger than the velocity in {s} , so that T m = T s . This leads to the Classical Velocity Addition Rule. T m
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8 Einstein’s way: velocity of light c is constant!
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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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Introduction to Modern Physics - Midterm Exam Exam will be...

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