PHY 2020 Lecture Notes - Lecture 43: Focal Length, Thin Lens, Sign Convention
Document Summary
Using trigonometry and law of refraction, we have: na/s + nb/s" = nb-na/r. If the center of curvature is on the outgoing side of the surface, then r>0. Example: a spherical fish bowl: a small tropical fish is at the center of a water-filled, spherical fish bowl 28. 0 cm in diameter. (a) find the apparent position and magnification of the fish to an observer outside the bowl. Light comes from the fish to the person"s eye (a) r= -14. 0 cm. s= +14. 0 cm na= 1. 333 (water). R=+14. 0 cm s"= 56. 0 cm s" is greater than the diameter of the bowl, so the surface facing the sunlight does not focus the sunlight to a point inside the bowl. The focal point is outside the bowl and there is no danger to the fish. Note: the rays refract when they exist the bowl back into the air so the image we calculated is not the final image.
