# I Why Planck's Constant Has Dimensions and a Unit?

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1. Oct 2, 2016

Despite being a constant, It has both dimensions and a unit, can someone kindly explain why ?

2. Oct 2, 2016

### Bystander

3. Oct 2, 2016

Planck's Constant is a dimensional constant. Energy= Planck's Constant. * frequency . It is not the only constant that has dimensions , many other physical constants also has dimensions , like gravitational constant.

4. Oct 2, 2016

### ZapperZ

Staff Emeritus
This question is puzzling. Are you saying that the property of a "constant" includes NO dimensions and NO units?

"c", the speed of light in vacuum, is a constant. It has "dimensions and units". Why are you not asking about that as well?

Zz.

5. Oct 29, 2016

Actually I intended to ask generally, but then I went for the example spontaneously, I have just studied units and dimensions and they told me that constants don't have dimensions and units, for example, number one itself, angle of measure 60° etc, and what came in my mind are constants which are in many relations in physics

6. Oct 29, 2016

### lychette

this is a LONG wikipedia reference....can you highlight the sections that you feel help in providing an explanation for this post?

7. Oct 29, 2016

### ZapperZ

Staff Emeritus
This makes very little sense. Who are these "they" that you are referring to?

The examples you cited are NOT "constants" in physics. These are simply numbers associated with some quantity. Again, look at "c". Do you think this constant has NO dimensions and NO units? This one constant itself falsify any claim that a constant has no dimension and no units.

Zz.

8. Oct 29, 2016

### phinds

As zapperz has pointed out, you are confusing terms. The examples you site are not physical constants, they are just numbers. If used in an equation, they can be called constants as far as math is concerned, but that has nothing to do with physical constants like c

9. Oct 30, 2016

### Redbelly98

Staff Emeritus
Simple answer: A constant may either have dimensions (i.e. units), or it may not.

Examples:
The fine structure constant alpha = 1/137.035... is a dimensionless physical constant.
And, as pointed out already in this thread, Planck's constant and the speed of light are constants that have units.