Physics 1220 In-Class Problems: Optical Instruments

1. The nearpoint of a farsighted person is 125 cm. What power contact lenses must this person wear to have "normal" vision?
2. If the person in Question #1 prefers glasses, what power should they be? Assume that the glasses are 2.00 cm from the eyes. 
3. If the person in Question #1 tries on contact lenses of power +2.5 diopters, where would his corrected nearpoint be?
4. The farpoint of a nearsighted person is 8.00 cm. What minimum power contact lenses should the person wear to be able to read a newspaper held 50 cm away from the eye?
5. A nearsighted person has a farpoint of 30.0 cm and a nearpoint of 8.5 cm. (a) What power should his contact lenses be? (b) What will be his corrected farpoint and nearpoint?
6. The nearsighted person in the previous problem puts in contacts of power –2.25 Diopters, what is his corrected farpoint and nearpoint?
7. A nearsighted person wears contacts of –3.50 diopters and can clearly see objects held 14.0 cm away. What is the uncorrected farpoint and nearpoint of this person?
8. If the person in Question #4 prefers glasses, what minimum power should they be. Assume that the glasses are 2.00 cm from the eyes.
9. A photographer is taking pictures on a bright sunny day with a camera shutter speed of 1/250 s and f/5.6. Suddenly the sky clouds over and the available light is reduced by three-quarters. (a) If only the shutter speed is changed, what new shutter speed would be needed for proper contrast? (b) If only the f-number is changed, what new f-number is needed?

10. The separation of the lenses in a compound microscope is 18.0 cm. The objective and eyepiece have focal lengths of 0.20 cm and 3.00 cm, respectively. (a) What magnification would a person with normal vision observe? (b) Where would the object have to be placed?

11. Galileo's telescope had a magnification of 3×. Assuming that the focal length of the eyepiece was 15 cm, how long was his telescope?

Questions? mike.coombes@kwantlen.ca