You use a camera with a lens whose focal length is 50.00 mm,and are taking a picture of a 2.500 m tall statue that is located 7.200 m from the lens.If the image height on the film is 18.20 mm,what is the distance from the lens to the film?
A) 5.035 cm
B) need more information
C) 6.32 mm
D) 5.242 cm

Question

Quizplus · Accepted Answer

Using the thin lens equation:

1/f = 1/di + 1/do

where f is the focal length, di is the distance from the object to the lens (7.200 m), and do is the distance from the lens to the image on the film (what we want to find).

We also know that the magnification of the image is equal to the ratio of the image height to the object height:

m = hi/ho = -di/do

where hi is the image height (18.20 mm) and ho is the object height (2.500 m).

Substituting the known values:

1/50 = 1/7.200 + 1/do

18.20/2500 = -7.200/do

Solving for do:

do = 5.242 cm

Therefore, the answer is D) 5.242 cm.

You Use a Camera with a Lens Whose Focal Length