# hw25 - Physics 21 Fall 2004 Solution to HW-25 34 P 5 How...

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Unformatted text preview: Physics 21 Fall, 2004 Solution to HW-25 34 P 5 How large is the image of the sun on the film used in a camera with (a) a 28 mm focal length lens, (b) a 50 mm focal length lens, and (c) a 200 mm focal length lens? The sun’s diameter is 1 . 4 × 10 6 km, and it is 1 . 5 × 10 8 km away. d o d i θ θ h i The single ray through the center of the lens shows that the angle subtended by the object is the same as the angle subtended by the image on the film. Since 1 d o + 1 d i = 1 f , one can see that as d o → ∞ , d i → f , so that for a dis- tant object that subtends a small angle, h i = f θ . From the information given θ = sun’s diameter sun’s distance = 1 . 4 × 10 6 1 . 5 × 10 8 = 9 . 33 × 10- 2 Evaluating h i = 9 . 33 × 10- 2 f for f = 28 mm, 50 mm, and 200 mm, we obtain h i = 0 . 26 mm, 0.47 mm, and 1.87 mm, respectively. 34 P 20 A 31.0 cm focal length converging lens is 24.0 cm behind a diverging lens. Parallel light strikes the diverging lens. After passing through the converging lens, the light...
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