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Unformatted text preview: Homework 7 Physics 204, evening summer 2008 Part 1 1. The distance from earth to the center of the galaxy is about 23500 ly (1 ly = 1 light‐year = 9.47 1015 m), as measured by an earth‐based observer. A spaceship is to make this journey at a speed of 0.9970c. According to a clock on board the spaceship, how long will it take to make the trip? Express your answer in years (1 yr = 3.16 107 s). 2. A space traveler moving at a speed of 0.59c with respect to the earth makes a trip to a distant star that is stationary relative to the earth. He measures the length of this trip to be 7.5 light‐years. What would be the length of this same trip (in light‐years) as measured by a traveler moving at a speed of 0.83c with respect to the earth? 3. A person on earth notices a rocket approaching from the right at a speed of 0.78c and another rocket approaching from the left at 0.60c. What is the relative speed between the two rockets, as measured by a passenger on one of them? 4. A spacecraft approaching the earth launches an exploration vehicle. After the launch, an observer on earth sees the spacecraft approaching at a speed of 0.55c and the exploration vehicle approaching at a speed of 0.80c. What is the speed of the exploration vehicle relative to the spaceship? Part 2 5. The maximum wavelength for which an electromagnetic wave can eject electrons from a platinum surface is 196 nm. When radiation with a wavelength of 141 nm shines on the surface, what is the maximum speed of the ejected electrons? 6. The interatomic spacing in a crystal of table salt is 0.282 nm. This crystal is being studied in a neutron diffraction experiment. How fast must a neutron (
moving to have a de Broglie wavelength of 0.282 nm? ) be 7. The dissociation energy of a molecule is the energy required to break apart the molecule into its separate atoms. The dissociation energy for the cyanogen molecule is . Suppose that this energy is provided by a single photon. Determine the (a) wavelength and (b) frequency of the photon. (c) In what region of the electromagnetic spectrum does this photon lie? 8. An electron, starting from rest, accelerates through a potential difference of 418 V. What is the final de Broglie wavelength of the electron, assuming that its final speed is much less than the speed of light? 9. A hydrogen atom emits a photon that has momentum with a magnitude of . This photon is emitted because the electron in the atom falls from a higher energy level into the n = 1 level. What is the quantum number of the level from which the electron falls? Use a value of for Planck’s constant. 10. A wavelength of 410.2 nm is emitted by the hydrogen atoms in a high‐voltage discharge tube. What are the initial and final values of the quantum number n for the energy level transition that produces this wavelength? ...
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This note was uploaded on 10/04/2009 for the course PHYS 750:204 taught by Professor Rollino during the Spring '09 term at Rutgers.
- Spring '09