A stretched string has a third harmonic frequency of 600 Hz. What is the frequency of the second harmonic?

Answer 1

I see a huge number of posts by the same poster. No work, no effort shown, just typing. Some apparently call for short papers. If you show some work on these and/or explain, in detail, what you don't understand about each, we may be able to help.

Answer 2

I thought diamond was the lowest index of refraction? Can you explain more?