Wolfram Research
Wolfram Math World: Harmonic Series
This MathWorld site provides a general overview of the harmonic series.
BBC
Bbc: Gcse Bitesize: Lenses
Lenses are precisely shaped pieces of glass that have been developed and used in corrective glasses, telescopes, microscopes, binoculars, and magnifying glasses. They can be convex or concave. Links are provided to a video an a test.
Math2
Math2.org: Series Expansions
A thorough review of calculus series. Links direct the student to the basic properties of series, as well as to explanations and examples of convergence tests in series. The expansions for exponential, logarithmic, and root functions and...
PurposeGames
Purpose Games: Plate Tectonics
Gamers will test their knowledge of plate tectonics with this interactive. Know your divergent plate boundaries, hot spots, trenches, lithosphere, and other trivial facts of plate tectonics.