A small cheap camera has a lens with a focal length of 5.20 cm. The camera is ar

Question

A small cheap camera has a lens with a focal length of 5.20 cm. The camera is arranged so that by moving the lens in or out, objects from 72.0 cm away to "infinity" can be brought to focus on the film.

a) At what distance from the film should the lens be placed so that images of far away objects come to focus on the film? Express your answer in centimeters.

b) How far should the lens be moved, from the position that results in a sharp image for far away objects, so that the closest objects form a focused image on the film? Express your answer in centimeters.

Explanation / Answer

A)

f = 5.20 cm .

object distance = do = infinite

using lens equation ::

1/f = 1/di + 1/do

1/5.20 = 1/di + 1/infinite

1/5.20 = 1/di + 0

so di = 5.20 cm

B)

f = 5.20 cm .

object distance = do = 72 cm

using lens equation ::

1/f = 1/di + 1/do

1/5.20 = 1/di + 1/72

so di = 5.60 cm

distance moved = d = 5.6 cm - 5.2 cm = 0.4 cm

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