A mirror with a focal length 20 cm has a 4.0 cm tall object placed 100 cm in front of it. What is the height of the image?
A)1.0 cm
B)1.6 cm
C)-16 cm
D)-1.0 cm
E)16 cm

Question

Quizplus · Accepted Answer

The mirror formula is 1/f = 1/v + 1/u. Here, f = 20 cm and u = -100 cm (object distance is negative for mirrors). Solving for v gives v = -25 cm. The magnification m = -v/u = -(-25)/(-100) = 0.25. The image height is m * object height = 0.25 * 4 cm = 1 cm. Since the image is inverted, the height is -1 cm.

A Mirror with a Focal Length 20 Cm Has a 4.0