# Can someone explain Planck's constant simply?

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## Solution 1

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\$.

## Solution 2

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.

## Solution 3

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.

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### Devin

Updated on December 06, 2020

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.

• Devin almost 8 years
I clarified my question.
• peterh almost 7 years
Considering the clarified form of the question, may I suggest a reopen vote?
• Spine Feast almost 8 years
or rather its numerical value, in Joules, is that energy
• peterh almost 8 years
@DepeHb Yes, of course. I extend my answer.
• Devin almost 8 years
So why is this used for many QM equations?
• BjornW almost 8 years
@Devin It's just a scalefactor, actually it can be made equal to 1 with proper choice of other units. So the h coefficient by itself isn't important qualitatively in QM really, the underlying structure is the same regardless, so even with h = 1 there will be waves and interference and the other strange QM stuff. You don't see it used in Newtonian physics, because it scales the size of QM waves. The simplest equation using it is probably E = h*f, that is, the scalefactor between energy and frequency for a photon as Peter writes above.
• peterh over 6 years
@Devin As I know, the Planck constant isn't really a parameter of the light, but a parameter of our Universe (similarly to the "c", which is also a "speed limit" in our universe). It is only the feature of the light that it goes always with the "speed limit". As I know, if there are gravitons, they would also propagate with c, and a 1Hz graviton has the same energy as a 1Hz photon.