# Optics lens problem

1. May 14, 2005

### Gshan12

i need help!!

Given: A real object is located to the left of a convergent lens. The object's distance from the lens is 7/3f and its focal length is f. What is the image distance in terms of f?

I tried the formula 1/f = 1/di + 1/do... it didn't work :grumpy:

2. May 14, 2005

### Staff: Mentor

What makes you think that doesn't work?

3. May 14, 2005

### Gshan12

i got a weird fraction that di= (1-3f^2)/(f^2) and it's not one of the answer choices.

4. May 14, 2005

### Staff: Mentor

I don't see how you get $f^2$. Redo it, carefully: $o = 7f/3$, so $1/o = 3/(7f)$. $1/i = 1/f - 3/(7f)$, etc.

5. May 14, 2005

### Gshan12

oh! i made a stupid math mistake...

THANK YOU SO MUCH!!