Question

Deep in the physics and astronomy basement storeroom, you find a very large concave spherical mirror from an old telescope. The mirror is 2 m across, and has a radius of curvature of 14.0 m. Because this is just a small piece of such a large sphere, the angle of incidence for on-axis rays will always be below 5°, minimizing spherical aberration You try out the mirror for use as a full-length wall mirror. If you look at yourself in the mirror from 2 m away, where will your image be formed, and how much will it be magnified or minified? (Include a ray diagram showing yourself, mirror, and image.) a) b) Unhappy with the wall mirror results, and noticing that the mirror is like a huge, very shallow bowl (only about 4 cm deep at center), you then decide to build a large birdbath! You set the mirror outside on a stand, facing straight up toward the sky. Within a few days, you find that you've created a solar furnace that has wounded a few unlucky birds at times when the sun was high overhead. At what distance from the mirror are birds in most danger, when there is no water in the bowl? Investigate the effect of filling the mirror with water: What is the new location of the focus, compared to its position when empty? Hint: trace a couple of reflected rays as they converge toward focus, with and without water in the bowl; use Snell's Law. (Include a ray diagram showing incoming, reflected, and refracted light.) c) Notes .The sun's rays are effectively parallel at the distance of Earth. For simplicity, treat the sun as shining down from directly overhead, though that never happens in Nebraska! Perhaps you built your birdbath someplace more tropical... Be sure to explain all of your answers as part of your narrative. Astonishing video of a solar furnace in action: http://www.youtube.com/watch?v z0 nuvPKIi8

Answer 1

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