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

AI Thread Summary
Planck's Constant is a dimensional constant, meaning it has both dimensions and a unit, which is essential for its role in physics equations, such as relating energy to frequency. The discussion highlights that not all constants are dimensionless; for example, the speed of light also has dimensions and units. There is confusion around the definition of constants, as some examples cited, like the number one or angles, are not considered physical constants. The distinction is made that while some constants may lack dimensions, many, including Planck's Constant, are defined with specific units. Understanding these differences is crucial for grasping the nature of physical constants in scientific contexts.
Nader AbdlGhani
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Despite being a constant, It has both dimensions and a unit, can someone kindly explain why ?
 
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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.
 
Nader AbdlGhani said:
Despite being a constant, It has both dimensions and a unit, can someone kindly explain why ?

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.
 
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ZapperZ said:
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.
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
 
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Nader AbdlGhani said:
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

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.
 
Nader AbdlGhani said:
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
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
 
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.
 
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