Lecture_20

Lecture_20 - Lecture 20-1 Lecture Classical Physics...

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Lecture 20 Lecture 20 -1 Classical Physics Continuous quantities are those which take on values in a continuous range without skipping any intermediate values. We have so far treated quantities like time, length, charge * , etc. as continuous. Classical physics deals with continuous quantities (for the most part). (Consider, e.g., displacement, velocity, energy, time, length, etc.) ¾ Mechanics (remember F = m a or K = (1/2)mv 2 ?) ¾ Electricity and Magnetism (remember Φ E = q enc / ε 0 ?) However, some things were not continuous numbers: 9 Charges on nuclei, ions, . .. Integer multiple of electroninc charge* 9 Order of interference fringes 9 Harmonics on a string
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Lecture 20 Lecture 20 -2 Quantization Discrete quantities are those that take on values from a discrete set (like {1, 2, 3, …} or {0.1,5,7/3, 1000}, for example). Number of apples sold in a market is a discrete quantity. In quantum physics , the dynamical variables like momentum, angular momentum, and energy are treated as discrete – these variables which are continuous in classical physics are quantized in quantum physics. This quantization is needed to explain the results of certain experiments which are otherwise impossible to understand.
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Lecture 20 Lecture 20 -3 Blackbody Radiation Puzzle ¾ Major difficulty in explaining by classical physics: ± Classical theory predicted the spectral intensity going up with frequency without limit: ultraviolet catastrophe ± In reality, the spectrum has a fixed shape with a single peak at the frequency T (in Kelvins).
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Lecture_20 - Lecture 20-1 Lecture Classical Physics...

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