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# 34 - Kapoor(mk9499 oldhomework 34 Turner(60230 This...

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Kapoor (mk9499) – oldhomework 34 – Turner – (60230) 1 This print-out should have 13 questions. Multiple-choice 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 left-hand 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 left-hand side and a radius of curvature of 8 . 6 cm on its right-hand side. 8 . 6 cm 17 . 8 cm What is the magnitude of the focal length of the lens? Correct answer: 31 . 3946 cm. Explanation: Basic Concept: The lens maker’s 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 maker’s 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 . AlternativeExplanation: 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 right-hand 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 doesn’t matter. The signs of both R 1 and R 2 change and the

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Kapoor (mk9499) – oldhomework 34 – Turner – (60230) 2 identity of both R 1 and R 2 interchange, if viewed from the opposite direction.
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