Which one is the Planck's constant?

1. Apr 26, 2005

Reshma

I have a minute problem here. Some of the QM books have treated $h$ as the Planck's constant while some $\hbar$ as the Planck's constant. So can someone resolve this difficulty for me? Thanks in advance!

2. Apr 26, 2005

JonoF

h-bar is 'Reduced Planck's Constant' or 'Dirac's Constant' (h/2pi).

Jono

3. Apr 26, 2005

James R

Both are often referred to as "Planck's constant". There's really no confusion, since two different symbols are used.

$$\hbar \equiv h / 2\pi$$

4. Apr 26, 2005

dextercioby

Planck's constant is $h$ and Dirac's constant is $\hbar$.The Bohr model of the atom is responsable for the "reduction" by $2\pi$ (because the orbits were circular).

Daniel.

5. Apr 26, 2005

Staff Emeritus
And also because the wave function is of the form $$e^{i\phi}$$ which defines the unit circle in the complex plane.

6. Apr 26, 2005

dextercioby

He asked about the origin of $\hbar$.I told him where it first appeared.Not the notation (that is due to Dirac,hence the name),but that $2\pi$.

In the context of quantum mechanics,it appears for the first time in Born & Jordan [1] commutation relations...

Daniel.

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[1]M.Born,P.Jordan,Zeits.f.Physik,34,858 (1925).

7. Apr 26, 2005

eNathan

May I ask. What is the purpose of Planks Constant $$p$$anyway? :woundering:

8. Apr 26, 2005

dextercioby

Proportionality constant between the energy of a quanta of radiation & the radiation frequency...?It has dimensions of action/angular momentum which is very important throughout any quantum theory.

Daniel.

9. Apr 27, 2005

Reshma

He? It is her! Anyway, thank you for the clarification. I realized that the older QM books have treated $$h$$ as Planck's constant while the latter versions have it as $$\hbar$$.

10. Apr 27, 2005

dextercioby

I'm sorry,but i think 'latter' versions use the word "reduced" when speaking of "eitchbar".

Daniel.

11. Apr 27, 2005

Reshma

Gasiorowicz's book on "Modern Physics" has not used the word "reduced" in particular. Anyway he was referring to same thing you mentioned I guess

Here is an excerpt:

12. Apr 27, 2005

dextercioby

I agree that not too many people use the syntagma 'Dirac's constant' when speaking about 'hbar'.But that doesn't justify in any way mixing up hystorical events...

Daniel.