Question

A. A concave mirror produces a real image that is three times as large as the object.
a) If the object is 22 cm in front of the mirror, what is the image distance?
b) What is the focal length of this mirror?

Answer 1

a) If the image is virtual, object must be between the mirror and it’s focal.

The ratio of image and object's distances gives us the ratio of their length.

Ho / Hi = ± Lo / Li

Ho=22 cm

Lo/Li = 1/3 (three times as tall as the object.)

Here, we find "the image distance" = 66 cm.

b) For focal length,

Ho=22 and Hi= -66 (minus because it is virtual)

1/Hi + 1/Ho = 1/F

F= + 33 cm