Question

1) A 6.47 mm high firefly sits on the axis of, and 11.5 cm in front of, the thin lens A, whose focal length is 6.11 cm . Behind lens A there is another thin lens, lens B, with a focal length of 20.7 cm . The two lenses share a common axis and are 61.5 cm apart. Is the image of the firefly that lens B forms real or virtual? What is the height of this image? Express the answer as a positive number (nm)?

image distance from lens B cm:

2)

One of the inevitable consequences of aging is a decrease in the flexibility of the lens. This leads to the farsighted condition called presbyopia (elder eye). Almost every aging human will experience it to some extent. However, for the myopic, or nearsighted, person it is possible that far vision will be limited by a subpar far point and near vision will be hampered by an expanding near point. One solution is to wear bifocal lenses that are diverging in the upper half to correct the nearsightedness and converging in the lower half to correct the farsightedness.

Suppose one such individual asks for your help. The patient complains that she can’t see far enough to safely drive (her far point dfar=114 cmd and she can’t read the font of her smart phone without holding it beyond arm’s length (her near point dnear=81.0 cm? Prescribe the bifocals that will correct the visual issues for your patient.

a)What is the focal length fns of the part of the bifocal lens that corrects the patient's nearsightedness?

b) What is the focal length ffsffs of the part of the bifocal lens that corrects the patient's farsightedness?

Answer 1