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.)