average (thinking about putting up a voting option) Introduction:
Of all the great discoveries in this world begin with the catch phrase "Thats easy." Most scientists would say this phrase is the gateway to greater understanding while many others laugh at the phrase.
Optics is a pretty solid field and just about most of it is figured out. However, that does not excuse it from spitting out the occational speed balls. The following problem is no exception.
Need to know:
-Fundemental understanding of thin lens behavior
-High school algebra
-Experience with units and pior problems
On a storming night of gools, you come across a magnifying glass of diameter 2 centimeters. On it theres a label stating the maximium magnification possible is x5 (size of image, not the image distance).
You, wanting to build a death laser would like to know what the focal length is. Unfortunately the only sources of light are comming from the lightning and the eyes following you. With no time to spare, whats the focal length of the magnifying glass?
As a bonus whats the general equation to find focal length?

To be added later(looking for a way to introduce a spoiler button). Though for now, I will say it becomes a function of diameter and magnification