Exam%203%20practice%20problems

# Exam%203%20practice%20problems - Exam#3 practice problems...

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Exam #3 practice problems Physics 204 summer 2008 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 (light years 0.20 ly 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. You are a member of a government sponsored think tank whose purpose is to investigate the future of weapons and defenses on the battlefield. Your group predicts that ultraviolet laser weapons will eventually replace projectile weapons and that windows (refractive index of 1. ) in vehicles will be particularly vulnerable. Your idea is to coat the windows with a transparent material with a refractive index of 1. and the appropriate thickness so it will completely reflect light. 60 80 200 nm a. Explain in detail why a transparent coating would be capable of completely reflecting light in the first place. b. What should the minimum thickness of the coating be? 4. A diffraction pattern is being created by an electron beam being sent through a rectangular gap of width . A detector located from the gap measures the first minimums of the pattern to be at ± . 20.0 nm 0.01 m 2.00 m a. How is this possible? Electrons aren’t the same as light. Why should they create any sort of diffraction pattern at all?

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Exam%203%20practice%20problems - Exam#3 practice problems...

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