A concave spherical mirror has a focal length of 12 cm.If an object is placed 18 cm in front of it the image position is:
A)7.2 cm behind the mirror
B)7.2 cm in front of the mirror
C)36 cm behind the mirror
D)36 cm in front of the mirror
E)at infinity

Question

Quizplus · Accepted Answer

Using the mirror formula: 1/f = 1/do + 1/di
where f = focal length, do = object distance, and di = image distance
Substituting the given values: 
1/12 = 1/18 + 1/di
Solving for di, we get: 
di = 36 cm
Since the image distance is positive, it is in front of the mirror. Therefore, the answer is D) 36 cm in front of the mirror.

A Concave Spherical Mirror Has a Focal Length of 12