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Unformatted text preview: Name __________________________ Student ID _______________ Score __________ Last First Phys 123A Exam III May 30, 2008 NOTE: In all Questions choose the answer that is the closest!! Question I. (20 pts) Interference and Diffraction 1. (5 pts) The spacing between the adjacent lines of a diffraction grating is the same as the distance between the two slits in the Young’s double slit experiment. Both are illuminated by light of the same wavelength. In which way do the interference fringes seen on the screen differ for the two methods? A. There is no difference in the interference fringes. B. The fringes from the grating are farther apart. C. Each of the fringes from the grating is narrower than those of the double slit. D. Each of the fringes from the double slit is narrower than those of the grating. E. The difference cannot be determined 2. (5 pts) Two identical rays of light start in phase and pass through two slits. For two rays that interfere destructively on the screen, their path lengths A. must be equal. B. must differ by an odd number of half wavelengths. C. must differ by an integral number of wavelengths. D. must differ by a quarter wavelength E. none of A thru D are correct 3. (5 pts) Two narrow slits are illuminated by monochromatic light. If the distance between the slits is equal to 2.75 wavelengths, what is the maximum number of dark fringes that can be seen on a very large screen? (A) 2 (B) 3 (C) 4 (D) 5 (E) 6 For maximum number of dark fringes to occur, sin θ =( n – 0.5) λ /(d) = 1 n =d/ λ + 0.5 n = (2.75 λ )/ λ + 0.5 = 2.75 + 0.5 = 3.25 ~ 3 since n must be an integer. So there are 3 dark fringes on either side of the central bright fringe; and thus a total of 6 can be seen. 4. (5 pts) An antenna for receiving television signals from a satellite has a diameter of 3 m. The signals have a wavelength of 24 m. If the diameter of the antenna is reduced to 50 cm, for what signal wavelength does the antenna still have the same angular resolution? (A) 4.0 m (B) 6.0 cm (C) 8.0 cm (D) 1.4 m (E) 24 cm Question II (25 pts) Quantum Mechanics 5. (5 pts) If the wavelength of an electron is equal to the wavelength of a proton, then (A) the speed of the proton is greater than the speed of the electron, (B) the speeds of the proton and the electron are equal, (C) the speed of the proton is less than the speed of the electron , (D) the Kinetic energy of the proton is greater than the Kinetic energy of the electron,...
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This note was uploaded on 07/01/2008 for the course PHYS 112 taught by Professor Wormer during the Spring '08 term at University of Washington.
- Spring '08