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Unformatted text preview: Kapoor (mk9499) oldhomework 34 Turner (60230) 1 This printout should have 13 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 (part 1 of 3) 10.0 points Assume: The object is on the lefthand side of the lens indicated in the figure below. A lens has an index of refraction of 1 . 53. The lens has a radius of curvature of 17 . 8 cm on its lefthand side and a radius of curvature of 8 . 6 cm on its righthand side. 8 . 6 c m 1 7 . 8 c m What is the magnitude of the focal length of the lens? Correct answer: 31 . 3946 cm. Explanation: Basic Concept: The lens makers equa tion is 1 f = ( n 1) parenleftbigg 1 R 1 1 R 2 parenrightbigg , where From the perspective of the object, R is positive if the center of curvature is behind a surface, otherwise R is negative . Given : n = 1 . 53 , R 1 = 17 . 8 cm , and R 2 = 8 . 6 cm . Solution: Applying the lens makers equa tion, 1 f = ( n 1) parenleftbigg 1 R 1 1 R 2 parenrightbigg = ( n 1) [ R 2 R 1 ] R 1 R 2 f = R 1 R 2 ( n 1) [ R 2 R 1 ] = ( 17 . 8 cm)( 8 . 6 cm) (1 . 53 1) [( 8 . 6 cm) ( 17 . 8 cm)] = 31 . 3946 cm , so (1)  f  = 31 . 3946 cm . 002 (part 2 of 3) 10.0 points The sign of the focal length is 1. Cannot be determined. 2. positive. correct 3. negative. Explanation: See Eq. 1 in the previous part for the sign of the focal length f . Alternative Explanation: Since the lens is thicker on axis than near its outer edge, the focal length f is positive and the lens is convergent. 003 (part 3 of 3) 10.0 points What are the changes to the magnitude and the sign of the focal length when the lens is flipped over (or alternatively, the object is on the righthand side of the lens)? 1. The magnitude increases and the sign is unchanged. 2. The magnitude decreases and the sign is unchanged. 3. The magnitude decreases and the sign changes. 4. The magnitude increases and the sign changes. 5. The magnitude stays the same and the sign changes. 6. The magnitude stays the same and the sign is unchanged. correct Explanation: The position of the object doesnt matter....
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This note was uploaded on 06/28/2009 for the course PHY 303L taught by Professor Turner during the Fall '08 term at University of Texas at Austin.
 Fall '08
 Turner
 Physics, Work

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