# Homework Help: Finding di and hi

1. Jul 9, 2014

### Capri

1. The problem statement, all variables and given/known data
Lawn spheres placed on pedestals are convex mirrors. One such sphere has a diameter of 40.cm. A 12 cm robin sits in a tree 1.5m from the sphere. Make a representative sketch. Where is the image of the robin? How long is the robins image?

2. Relevant equations
1/f=1/di+1/do
hi/ho=-di/do

3. The attempt at a solution
I have a diagram but am stuck on where to go from here?

2. Jul 9, 2014

### collinsmark

Hello Capri,

Welcome to Physics Forums!

First, work your way to finding the focal length of the mirror.

You know the diameter of the sphere. From that, you can determine the radius of curvature*. From there you should be able to look up some formula for the focal length as a function of the radius of curvature. Oh, and don't forget to pay attention to the +/- sign and how that relates to concave or convex mirrors.

*[Edit: radius of curvature is often called center of curvature.]

Last edited: Jul 9, 2014