# How far are you from this lens

1. Jan 26, 2010

### binhnguyent9

1. The problem statement, all variables and given/known data
You are standing in front of a lens that projects an image of you onto a wall 2.80 {\rm m} on the other side of the lens. This image is three times your height.
How far are you from the lens?
Is your image erect or inverted?
What is the focal length of the lens?
Is the lens converging or diverging?

2. Relevant equations

none

3. The attempt at a solution
none

thanks a lot for your help

2. Jan 26, 2010

### rl.bhat

Re: Lens

Which lens produces real magnified image?
What is the realtion between the objectg distsnce, image distance and magnification?

3. Jan 26, 2010

### binhnguyent9

Re: Lens

well the convex len can produce a real image, and m=-image distance/ object distance. i have try everything, and i don't know why it keep tell me i am wrong, if you don't mind can you do one of the part, then i can check it? thanks a lot for your help

4. Jan 26, 2010

### rl.bhat

Re: Lens

Image distance is given. Magnification is given. Find the object distance.
Use the formula
1/do + 1/di = 1/f
For real image di is +ve.
And for virtual image di is -ve.

5. Jan 26, 2010

### binhnguyent9

Re: Lens

oh ok, thanks a lot. i think i misread the question first. thanks so much for your help