Where will this image be located?

Question

 The equation connecting s, p, and f for a simple lens can be employed for spherical mirrors, too. A concave mirror with a focal length of 7 cm forms an image of a small object placed 11 cm in front of the mirror. Where will this image be located?

Answer 1

Hello Emma!

Using the spherical-mirror equation which states that 1/f = 1/do + 1/di where f is the focal length, do is the distance the object is from the mirror, and di is the distance the image is from the mirror:

1 / 7 = 1 / 11 + 1 / di

Assuming the convention that a concave mirror has a positive f and an object in front of the mirror has a positive do. We see that di is + 19.25 cm in front of the mirror.

Hope that helps!