A concave mirror having a focal length of magnitude 5.0 cm forms an image 4.0 cm behind the mirror. Where is the object for this image?
A) 2.2 cm behind the mirror
B) 2.2 cm in front of the mirror
C) 1.0 cm behind the mirror
D) 9.0 cm in front of the mirror
E) 20 cm behind the mirror

Question

Quizplus · Accepted Answer

The image is formed 4.0 cm behind the mirror, which means it is virtual and upright. Using the thin lens equation, 1/f = 1/do + 1/di, where f is the focal length, do is the object distance, and di is the image distance, we can solve for do:1/5 = 1/do + 1/(-4)1/do = 1/5 + 1/41/do = 9/20do = 20/9 = 2.2 cmTherefore, the object is 2.2 cm in front of the mirror.

A Concave Mirror Having a Focal Length of Magnitude 5