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Unformatted text preview: gilbert (amg3448) HW11 tsoi (57210) 1 This printout should have 18 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points Will the light from two very close stars pro duce an interference pattern? 1. Yes; strong light from the two stars cre ates very clear interference patterns. 2. No; the light is too strong to produce a discernable interference pattern. 3. No; light from two very close stars is not likely to have the same frequency. correct 4. Yes; if they are very close to each other, the light has large overlapping area. Explanation: Light from a pair of stars will not produce an interference pattern because the waves of light from the two separate sources have dif ferent frequencies and thus are incoherent; when combined they smudge. Interference occurs when light from a single source divides and recombines. 002 10.0 points A laser beam of wavelength 554 nm is incident on two slits. y 5 . 51 m . 2mm S 1 S 2 viewing screen Approximately how far apart will be the bright interference fringes on the viewing screen? Correct answer: 0 . 0152628 m. Explanation: Let : = 554 nm = 5 . 54 10 7 m , L = 5 . 51 m , y = 0 . 0152628 m , and d = 0 . 2 mm = 0 . 0002 m . r 2 r 1 y L d S 1 S 2 = ta n 1 y L viewing screen d sin r 2 r 1 P O S 2 Q S 1 90 Q The condition for constructive interference is d sin = m , where m = 0 , 1 , 2 , , . so the angle be tween the bright interference fringes measured from the center of the double slits is = arcsin d = arcsin 5 . 54 10 7 m . 0002 m = 0 . 15871 . Therefore, the distance between the bright interference fringes is y = L tan = (5 . 51 m) tan(0 . 15871 ) = . 0152628 m . 003 10.0 points A screen is illuminated by monochromatic light as shown in the figure below. The distance from the slits to the screen is L . y L d S 1 S 2 viewing screen gilbert (amg3448) HW11 tsoi (57210) 2 Using the small angle approximation ( = sin = tan ) , what is the wave length if the distance from the central bright region to the seventh bright fringe is y . 1. = 1 8 L y d 2. = 2 13 L y d 3. = 1 8 d y L 4. = 2 13 d y L 5. = 1 7 d L y 6. None of these. 7. = 2 13 d L y 8. = 1 8 d L y 9. = 1 7 L y d 10. = 1 7 d y L correct Explanation: Basic Concepts: For bright fringes, we have = d sin = m , and for dark fringes, we have = d sin = m + 1 2 , where m = 0 , 1 , 2 , 3 , . From geometry, we have y = L tan . r 2 r 1 y L d S 1 S 2 = ta n 1 y L viewing screen d sin r 2 r 1 P O S 2 Q S 1 90 Q r 2 r 1 d S 1 S 2 = ta n 1 y L d s i n r 2 r 1 S 2 Q S 1 9 Q Solution: The angle from the slits mid point to the y position on the screen is = arctan y L ....
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This note was uploaded on 03/29/2012 for the course PHY 302l taught by Professor Morrison during the Spring '08 term at University of Texas.
 Spring '08
 morrison
 Physics

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