# Homework Help: Newton's Rings Help

1. Mar 3, 2006

### Knicks685

Hi. I have some homework questions here that I need a little help on. I know the fomulae to use just do not know how to apply it properly. Any help will be appreciated.

In a Newton's Ring experiment, a planoconvex glass (n=1.54) lens having a diameter 14.3 cm is placed on a flat plate. When 585 nm light is incident normally, 8 bright rings are observed with the last one right on the edge of the lens, at r.

1. What is the thickness of the lens?
2. What is the radius of curvature of the convex surface of the lens?
3. What is the focal length of the lens?

2. Mar 3, 2006

### BananaMan

not that i can answer this but if you read the FAQ you are supposed to show some working or some effort to have started your problem, maybe if you do that you will have more of a chance of it being answered

3. Mar 4, 2006

### Knicks685

Well I know that at the center there is a dark spot so to find the thickness of the lens I'd assume that t=m(lambda)/2n but I get an unreasonable answer. To find the radius of curvature I tried using r=sqroot(m(lambda)R/n therefore R=r^2/(m*lambda*n) but again I don't think I'm getting the right answer. I'm not trying to catch a break here. So any help will be appreciated.