1. Lenses and Refraction Which type of lens has a focal length that is always negative? ans: diverging or concave lens If the focal length of a concex lens is 10 mm where is an image formed if the object is placed at 20 mm? ans: Case #3, 20 mm s 2x focal length Which lens is thick at the ends and thin in the middle? ans: concave

2. With which index of refraction is the light bent most? n = 1.55 or n = 1.12. Justify! n 1.55 b/c increase in optical density Which case # for image formation has an image formed beyond 2F when the object is placed between F and 2F? ans: Case #4 Which case # for mage formation yields NO mage formed? ans: Case #5

3. When is a concave and a convex lens alike with respect to image formation? ans: Case #6 both form virtual images True or False: An increase in the optical density means the refracted ray will bend more away form the normal? ans: False True or False: The index of refraction for a uniform medium is a constant? ans: True

4. Which case # for image formation is the image enlarged and both the object heigth and the image height are positive? ans: Case #6 A single ray of light travels from a n = 1.33 to a medium with n = 1.52. Which will have the small angle from the normal? ans: 1.52 Which type of lens is thick in the middle and tin at the edges? ans: convex

5. What determines the focal point for a lens? ans: curvature of the lens What do you get when light refracts from greater optical density to lesser optical density past the critical angle? ans: internal reflection What type of lens is in the human eye? ans: Convex You have a lens. At any position relative to the object, the image is upright. What type of lens do you have? ans: concave

6. A convex lens has a focal length of 15 cm, if the object is place at 30 cm, where is the image formed? ans: at 30 cm, Case #3 A convex lens has a focal length of 10 cm, if the object is placed at 15 cm, where is the image formed? ans: at 30 cm, Case #4 Which type of lens can NOT start a fire? ans: concave or diverging lens

7. An image is formed at 18 cm by a converging lens that has a focal length of 12 cm. Where is the object located? If the image is measured to 1.5 cm, what is the height of the object? Is the image real or virtual, upside down or upright with respect to the object?

8. What is the angle of refraction as a ray of light travels from the water (n= 1.33) into the air (n = 1.0) with a angle of incident of 20 o ? A ray of light has an angle of incident in air (n = 1.0) is 23 o into water ( n = 1.33) and then into an unknown medium where the ray is bent to 14.9 o from the normal. What is the index of refraction of the unknown medium and what is the unknown medium?

9. An object is placed 15 cm in front of a diverging lens that forms an image on the same side as the object at 7.5 cm. The height of the image is measured to 1.3 cm. What is the focal length of this lense? What is the height of the object?