Tan's face is 20 cm in front of a concave shaving mirror. If he observes his image to be twice as big and upright, what is the focal length of the mirror?
A) 40 cm
B) 10 cm
C) -50 cm
D) 50 cm
E) -40 cm

Question

Quizplus · Accepted Answer

The image is twice as big and upright, which means the mirror is concave and the object is between the pole and the focal point. Using the mirror equation, 1/f = 1/v + 1/u, we can find the focal length: 1/f = 1/20 + 1/10 = 3/20, so f = 20/3 = 6.67 cm. The closest choice is A) 40 cm.

Tan's Face Is 20 Cm in Front of a Concave