# Problems : Refraction and Snell’s Law, Image formation by thin lenses

1. A contact lens is made of plastic with an index of refraction of 1.50. The lens has an outer radius of curvature of  +2.00 cm and an inner radius of curvature of +2.50 cm. What is the focal length of the lens?
2. A double-convex lens is to be made of glass with an index of refraction of 1.5. One surface is to have twice the radius of curvature of the other and the focal length is to be 50 mm. What is the (a) smaller and (b) larger radius?
3. An object is 20 cm to the left of a thin diverging lens that has a 30 cm focal length. (a) What is the image distance? (b) Draw a ray diagram showing the image position.
4. A cubical block of ice 50.0 cm on a side is placed on a level floor over a speck of dust. Find the location of the image of the speck as viewed from above. The index of refraction of ice is 1.309.
5. An antelope is at a distance of 20.0 m from a converging lens of focal length 30.0 cm. The lens forms an image of the animal. If the antelope runs away from the lens at a speed of 5.00 m/s, how fast does the image move? Does the image move toward or away from the lens?