Exam 3 practice problems

Exam 3 practice problems - Exam #3 practice problems...

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Exam #3 practice problems Physics 204 1. NASA makes an announcement that the Hubble Space Telescope has detected a signal from an alien probe. When the probe sent the signal it was 0.20 ly (light years 1 ) away and headed towards Earth at 0.75 c . a. By the time the signal reaches Earth how far away is the probe? How much time will pass on earth between the signal being received and the probe arriving? b. At the moment the probe sends the signal, how far away does the probe detect the earth to be? c. From the moment the probe sends the signal, how long will the probe take to reach the earth according to its own clock? 2. In order to investigate the alien probe featured in the previous problem NASA launches a probe of its own. It speeds away from Earth at 0.60 c . a. How fast is the alien probe moving relative to NASA’s probe? b. Unfortunately the alien probe is highly maneuverable and slips past NASA’s probe. NASA’s probe turns around and pursues the alien probe but can’t keep up due to its slower speed. How fast is the alien probe moving relative to NASA’s probe now? 3. A diffraction pattern is being created by an electron beam being sent through a rectangular gap of width 20.0 nm . A detector located 2.00 m from the gap measures the first minimums of the pattern to be at 0.01 m . a. How is this possible? Electrons aren’t the same as light. Why should they create any sort of diffraction pattern at all? b. What is the speed of the electrons in the beam? 4. One of the most striking discoveries of the early 20 th century in physics was that light and matter both exhibit wave- like and particle-like behaviors. Give experimental evidence for each of these four phenomena. Describe each of these pieces of evidence in sufficient detail so that it is clear why it is evidence for that particular behavior. 5. When astronomers look at nebulae (which are glowing interstellar clouds of gas) they can use their color to determine their chemical composition. When a nebula appears red (remember, the visible part of the spectrum is from 400 to 700 ) they know it is because light of a very specific wavelength is being produced by large amounts of hydrogen in the nebula. Explain specifically what is happening to the hydrogen that causes the nebula to appear red and predict numerically the wavelength of this red light. 6. Antireflective coatings are used on camera lenses to allow more light into the camera which results in a better picture than if the lens had no additional coating. Any transparent material will work provided the correct thickness is used, though generally the material is chosen so that the index of refraction is greater than that of air ( 1.00 air n ) and less than that of the camera lens ( 1.50 lens n ). So, imagine that you have a camera lens with an antireflective coating that has an index of refraction of 1.20.
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Exam 3 practice problems - Exam #3 practice problems...

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