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 Jun 11th 2009, 06:24 PM #1 Junior Member   Join Date: Jun 2009 Posts: 1 Help me PLZ I NEED IT BY TONIGHT!! Hi, Bunch of problems.... 1. (critical angle) A small pebble lies at the bottom of a tank of water 24 ft deep. Determine the size of a piece of cardboard which, when floating on the surface of the water, directly above the pebble, totally obscures the pebble from view. 2. (apparent depth) A person lying at poolside looks over the edge of the pool and sees a bottle cap on the bottom directly below, where the depth is 3.2m. How afar below the water surface does the cap appear to be? 3. (Lensmaker Equation) A symmetric double convex lens with a focal length of 25 cm is to be made from glas with an index of refaction of 1.52. What should be the radius of curvature for each surface? Please help me.!!
Jun 14th 2009, 06:27 PM   #2
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 Originally Posted by jkhwun Hi, Bunch of problems.... 1. (critical angle) A small pebble lies at the bottom of a tank of water 24 ft deep. Determine the size of a piece of cardboard which, when floating on the surface of the water, directly above the pebble, totally obscures the pebble from view. 2. (apparent depth) A person lying at poolside looks over the edge of the pool and sees a bottle cap on the bottom directly below, where the depth is 3.2m. How afar below the water surface does the cap appear to be? 3. (Lensmaker Equation) A symmetric double convex lens with a focal length of 25 cm is to be made from glas with an index of refaction of 1.52. What should be the radius of curvature for each surface? Please help me.!!
1. Find the critical angle of water. Then tanC = R/d where R is the radius of the cardboard and d is the depth of the pebble.
2. Problem is not clear. Draw the diagram.
3. Find the len's maker's formula and find R.

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