A object is 12 cm in front of a concave mirror, and the image is 3.0 cm in front of the mirror. What is the focal length of the mirror?
A) 0.25 cm
B) 15 cm
C) 4.0 cm
D) 2.4 cm
E) 1.3 cm

Question

Quizplus · Accepted Answer

The image is virtual and upright, so the mirror is concave. The magnification is -1, so the object and image are the same size. The object distance is 12 cm, and the image distance is 3 cm. The focal length is given by the equation 1/f = 1/do + 1/di, where do is the object distance and di is the image distance. Substituting the given values into the equation, we get 1/f = 1/12 + 1/3 = 5/12. Therefore, the focal length is f = 12/5 = 2.4 cm.

A Object Is 12 Cm in Front of a Concave