# Converging Lenses

1. Feb 20, 2004

### raiieanna

I am having trouble with my homework. I know the answer but I can't figure out how to get there. The question is "An image of a flower is produced on a screen by a lens 1.60m from the screen. The image of the flower has a linear magnification of -2.5. What is the focal point of the lens?" I know the 1/o + 1/i = 1/f. I also know that
m = -i/o. Also, the image distance 1.6m. So, shouldn't -2.5=-1.6/o? But when I do this I get the wrong answer! Please help me!

2. Feb 20, 2004

### Integral

Staff Emeritus
You have
$$\frac 1 o + \frac 1 i = \frac 1 f$$
and
$$-2.5 = -\frac i o$$
and
$$i= 1.6m$$
so
$$i = 2.5 o$$
$$1.6m = 2.5o$$
$$o = \frac {1.6} {2.5}m$$

Can you finish it now?