# Convex Mirrors and Magnification

1. May 24, 2009

### kc262

1. The problem statement, all variables and given/known data
What is the image distance for an automobile 4.5 m in front of a convex miror with a 0.15 m focal length? I found this to be 0.155 m

The question I'm having a problem with is: What is the magnification?

2. Relevant equations

magnification = - (image distance/object distance)

3. The attempt at a solution

I thought it would simply be,
-[0.155m/4.5m] = -0.0344. But it's not.

Some help would be much appreciated

Last edited: May 24, 2009
2. May 24, 2009

### Staff: Mentor

Careful with signs. For a convex mirror, what sign will the focal length have?

3. May 24, 2009

### kc262

I realized that because it is a convex mirror, the focal length would be negative. However the marking program marked my answer right. I was confused by this And because of this discrepancy, I am unsure of how to find the magnification.

4. May 25, 2009

### Redbelly98

Staff Emeritus
Is the image real or virtual? (And therefore, is the image distance positive or negative?)

5. May 25, 2009

### Staff: Mentor

Then how did you get an image distance of +0.155 m ? (See Redbelly98's comment.)