# Finding image location with concave mirror

1. Apr 7, 2012

### physiquephys

1. The problem statement, all variables and given/known data
A small object is located 32.0cm in front of a concave mirror with a radius of curvature of 40.9cm.
Where will the image be formed?

2. Relevant equations

tan(θ)=-h/di
f=1/2R?

3. The attempt at a solution

Haven't been able to solve for theta. I'm not sure what equation to use, but I'm guessing that the radius is important. Do I need to find the focal length?

2. Apr 7, 2012

### Redbelly98

Staff Emeritus
Welcome to Physics Forums.

Yes, you need to find the focal length first. And, your text book should have a formula that relates focal length to the positions of the object and image, that will be helpful here.

3. Apr 7, 2012

### Emilyjoint

you do need to know the focal length. You have to be careful with equations. focal length =R/2 not....1/2R....do you see what I mean/

4. Apr 9, 2012

### physiquephys

Ohhhh, I see. I use 1/do + 1/di = 2/R (which is the focal point, & the reason the difference is indicated). Thank you both!

5. Apr 9, 2012

### Redbelly98

Staff Emeritus
Yes, that's the idea. You're welcome!