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.
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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