- #1
wg1337
- 11
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Homework Statement
I have an actually interesting practical homework. I need to calculate the optical strength (hope I translated it right, D=1/F), to do I need to find the lens focal length. I need to find my self a concave and a convex lens. I don't have a concave lens (I think), but I do have a 200mw laser with and convex lens, so one part I can do. I don't know how could I find the focal length for concave and I don't seem to know where to get such a lens.
Homework Equations
For convex lens I could simply use D=1/F, so if I put my laser bit away from a sheet of paper and if the paper burns (my laser can do it) then it is the focal length.
For concave lens I could use this: D=1/f + 1/d, where f is length to screen and d is length to object and magnification is f/d.
The Attempt at a Solution
I think my way with finding focal length with laser is enough good, but maybe there is a better way.
But I don't like my idea about how to get focal length for concave lens:
I use the laser and let it go trough this lens, I move the lens/laser away to find when the laser dot is, for example, 10 times bigger. But don't know really how would it work.
Any better ideas?
Where could I find (in some device maybe) a concave lens?