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Unformatted text preview: Howard (clh2528) Homework #2 shubeita (57885) 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 2) 10.0 points An object located 32 . 5 cm in front of a lens forms an image on a screen 10 . 5 cm behind the lens. Find the focal length of the lens. Correct answer: 7 . 93605 cm. Explanation: Basic Concepts: 1 p + 1 q = 1 f m = h h = q p Converging Lens f > >p> f f <q < >m> f >p> <q < >m> 1 Diverging Lens f < >p> f <q < <m< 1 Solution: The formula relating the focal length to the image distance s and the object distance s is 1 s + 1 s = 1 f so f = ss s + s = (32 . 5 cm) (10 . 5 cm) (32 . 5 cm) + (10 . 5 cm) = 7 . 93605 cm . 002 (part 2 of 2) 10.0 points What is the magnification of the object? Correct answer: . 323077. Explanation: Magnification is M = s s = (10 . 5 cm) (32 . 5 cm) = . 323077 . 003 10.0 points S E F W P Q Which of the glass lenses above, when placed in air, will cause rays of light (par allel to the central axis) to converge ? 1. F, S, and E 2. F, Q, and P 3. S and E 4. S and Q 5. F, W, and E 6. F, W, and Q correct 7. F, S, W, and P 8. F, E, and P 9. W and Q 10. F, S, Q, and P Explanation: convergent divergent Use the lens makers equation 1 f = ( n 1) parenleftbigg 1 R 1 1 R 2 parenrightbigg , where R 1 and R 2 are + (or ) if the center of curvature is behind (or in front of) the lens. To cause parallel rays of light to converge, f must be positive ( n > 1). Howard (clh2528) Homework #2 shubeita (57885) 2 F: R 1 > 0 and R 2 = , = f > , therefore convergent. S: R 1 = and R 2 > 0, = f < , therefore divergent. W: R 1 > 0 and R 2 > 0, but  R 1  >  R 2  , = f > , therefore convergent. E: R 1 < 0 and R 2 < 0, but  R 1  <  R 2  , = f < , therefore divergent. Q: R 1 < 0 and R 2 < 0, but  R 1  >  R 2  , = f > , therefore convergent. P: R 1 > 0 and R 2 > 0, but  R 1  =  R 2  , = f = , therefore neither convergent or divergent. Thus, lenses F, W, and Q are convergent lenses and Lenses S and E are divergent....
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 Spring '08
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