Chapter5-1 - First Exam Friday, Oct 7! 50 minutes, in...

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Unformatted text preview: First Exam Friday, Oct 7! 50 minutes, in class. Covers Chapters 1-4 You will need a calculator Closed book You may bring one 8 x 11 formula sheet No cell phones, laptops, PDAs or other wireless Bring ID Light and Telescopes Chapter 5 Astronomical Telescopes Primary objective: to gather large amounts of light => large telescopes! The Gemini-North optical telescope on Mauna Kea in Hawaii stands over 19 m (60 ft) high, and the primary mirror at the bottom is 8.1 m (26.5 ft) in diameter. Other forms of radiation (other than visible light) can also be observed, but very different telescope designs are needed. Radiation: Information from Space The Electromagnetic Spectrum In astronomy, we cannot perform experiments with our objects (stars, galaxies, ). The only way to investigate them is by analyzing the light (and other radiation) they emit. Light as a Wave (I) Light waves are characterized by a wavelength and a frequency f. f = c/ c = 300,000 km/s = 3 108 m/s f and are related through Wavelength: distance between wave peaks Thought Experiments What is the relative speed between you and the other car? Answer: 35m/s - 25 m/s = 10 m/s Car You 35m/s 25m/s Thought Experiments What is the relative speed between you and the beam of light? Answer: 300,000,000m/s - 25 m/s = 299,999,975 m/s ? No! Real Answer: 300,000,000 m/s Flashlight at rest You 300,000,000m/s 25m/s Relativity Principle of relativity (Galileo) If the Earth moves, why dont we get left behind? velocities are relative moving observer only sees velocity difference no absolute state of rest (only with respect to something) Motion is relative Galilean Transform : Speed of Light Changes Assume a light pulse is created on a moving train (in frame S). Light velocity in frame S is c . What is the lights velocity observed in Earth frame S? According to Galilean transform, velocity in frame S is c + v ! S S c v NO Preferred Reference Frame for Light! In 1800s, scientists thought that light propagated through some type of ether . Michelson-Morley Experiment (1887) Test if ether exists and sets preferred reference frame. Analogous to rowboat in river. Measure light speed relative to earths motion (// and ) using an interferometer (fringes). Result : No detection of ether No detectable shift in interference fringes occurred, indicating that light speed DID NOT depend on direction . Special Relativity : Postulates Principle of Relativity All the laws of physics are the same in all inertial reference frames, i.e. frames moving at constant velocities w/respect to each other....
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This note was uploaded on 10/17/2011 for the course PHY 121 taught by Professor Weinstein during the Fall '08 term at SUNY Buffalo.

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Chapter5-1 - First Exam Friday, Oct 7! 50 minutes, in...

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