Can someone explain Planck's constant simply? Can someone explain Planck's constant simply?
I know the math, however I don't understand the relevance. 
To explain what I'm asking, what is the significance of it when doing quantum mechanical calculations such as getting Planck length or other such equations.
 A: Others will probably answer much more complex versions, and they will explain much better. But here is a very simple answer:
Its numerical value is the energy of a single photon with the frequency of $1 Hz$.
A: From another point of view, you can see $h$ as a spatial and temporal scale factor where quantum wave effects become more or less relevant. Changing h is like "zooming in/out"; if you reduce $h$, it's like zooming out, at which point quantum waves oscillate in such a small scale that their interference effects average out into a more classical world.
This way of seeing it can be useful for intuition.
A: After people understood that there is something wrong with electromagnetic wave (a classical concept and description), the photon came in (search for black-body radiation and ultraviolet catastrophe for details). Here is the rule of Mr. Planck, he stated that the energy of this photon is proportional to the frequency associated with it and the constant that relates these two is Planck Constant.
With this new condition, Planck had imposed the quantization of the energy of the oscillators, "a purely formal assumption … actually I did not think much about it…" in his own words.
