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by: Sophie Stella

physnotesweek5.pdf PHYS 104-01

Sophie Stella

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Here are the notes for the 5th week of PHYS 104, Astronomy with Dr. Ruch.
Dr. Ruch
Class Notes
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This 2 page Class Notes was uploaded by Sophie Stella on Tuesday March 29, 2016. The Class Notes belongs to PHYS 104-01 at University of St. Thomas taught by Dr. Ruch in Winter 2016. Since its upload, it has received 32 views. For similar materials see Astronomy in Astronomy at University of St. Thomas.

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Date Created: 03/29/16
PHYS 104: Astronomy Week 5 Course Notes, 2/29 – 3/4 Definitions The Speed of Light: c=186,000 miles per second (671 million mph). Nothing can be faster than c. This is the same for any reference frame. Medium:Any substance. In context, it means that which allows waves to propagate (move). Ether: Atheory (developed by Maxwell) for the medium through which light moved when it acted as a wave. This theory was disproven. Reference Frame: The point of view of a closed system from any given reference point. There is no absolute rest frame. V. Special Relativity A. The Speed of light 1. Galileo tried to track the speed of light with his pulse, but was convinced that light is instantaneous. 2. Maxwell's theory: Light is a wave, which propagates through the Ether, and the speed of light is the same for any observer. a. Waves must propagate through a medium of some sort. If Light is a wave, it must propagate through a medium in space. Maxwell called this the Ether. b. The velocity of a wave is determined by the medium through which it is moving. (If one is in motion with respect to a medium, one would add one's velocity to the propagation velocity.) c. Michelson and Morley tested this theory, and found that the Earth's velocity with respect to the Ether is zero. If the Ether existed, this wouldn't be possible, so they therefore determined that the Ether does not exist. B. Inertial Reference Frames 1. If a closed system's velocity is constant, it is impossible to tell that it is in motion except from outside the system. (acceleration = 0, v--->) 2. If the closed system is accelerating, there are ways in which one can detect that it is in motion from within. (a--->, v--->) 3. There is no absolute rest frame. If there are two objects with a constant velocity relative to one another, it is valid to pick either as the rest frame. a. This is only true for objects with constant velocity. 4. Asystem's velocity is additive a. Objects within a system moving at a given speed with respect to each other must be added to get the relative speed for a reference frame outside the system. 5. Light is not additive a. Light remains the same speed with respect to all reference frames. The speed of light is the same for any observer. The laws of physics are identical for any frame of reference. 6. The distance traveled is different depending on the reference frame. a. v=d/t (velocity equals distance over time) If distance df (fixed)>dm (moving), then velocity vf>vm. This is not the case for light! According to Einstein, d=ct, where c (the speed of light) is a fixed velocity. This means that if df>dm, then time tf>tm. Time moves slightly faster from the point of view of a fixed frame. VI. Quantum Mechanics A. Light 1. “Color” refers to the frequency or wavelength of the light being reflected off an object. 2. All the wavelengths on the graph are light, but only the “visible light” is detected by our eyes. 3. Light behaves both like a wave and like a particle. B. Einstein and the photoelectric effect 1. Alight's intensity refers to the number of photons (light particles). 2. Color is determined by the speed of the photons (red is slower, violet is faster). C. Atomic Structure 1. Excited atoms selectively emit photons. a. electrons are waves of negatively charged energy, and their orbits are wavelengths. a. excited electrons are electrons that speed up due to temperature fluctuation or collision of other particles.


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