Two thin lenses,with focal lengths of 22.0 cm and -40.0 cm are placed in contact in an orientation so that their optic axes coincide.What is the focal length of the two in combination? {Hint: A thin lens is one whose thickness is negligible).

Question

Quizplus · Accepted Answer

For two thin lenses in contact, the combined focal length can be found using the equation:
1/f = 1/f1 + 1/f2 - d/f1f2
where f1 and f2 are the focal lengths of the individual lenses and d is the distance between them (which is negligible in this case).

Substituting values, we get:
1/f = 1/22 + 1/-40 - 0/(22 x -40)
1/f = 0.0455 - 0.025
1/f = 0.0205

Therefore, f = 48.9 cm, which is option D.

Two Thin Lenses,with Focal Lengths of 22