A building 30 m tall is being photographed with a camera with a lens of focal length 50 mm.How tall is the image on the film if the building is 100 m away?
A) 30 mm
B) 15 mm
C) 10 mm
D) 3.0 mm
E) 1.0 mm

Question

Quizplus · Accepted Answer

Using the formula for thin lens magnification (m = -d_i/d_o), where m is the magnification, d_i is the image distance, and d_o is the object distance:

m = -f/d_o

where f is the focal length.

We know that the object distance d_o is 100 m and the focal length f is 50 mm = 0.05 m. So:

m = -0.05/100 = -0.0005

This means that the image height is 0.0005 times the object height. The object height is 30 m, so:

image height = 0.0005 * 30 = 0.015 m = 15 mm

Therefore, the answer is B.

A Building 30 M Tall Is Being Photographed with a Camera