# Numbers and Constants

1. Dec 30, 2003

### Mk

What is the purpose of all the Planck's stuff? Planck's length, Planck's energy. And what is Boltzman's constant? On my calculater (PCalc 2 for mac) what is the "Universal Gas" (8.31451)?

2. Dec 31, 2003

### Integral

Staff Emeritus
The various "Planck" quantities are arrived at by manipulation of Planck Constant, which is an indication of the smallest units of energy. (Sort of like Universal pennies)

The numbers are not what you should be looking at when you come upon a "constant". You give the number associated with the Gas constant, it is meaningless without the UNITS.

The gas constant is the R in

PV= nRT, the exact number will depend on the units of the other quantities. To get meaningful results the units must be correct.

Boltzmann constant is related to the Gas constant, it is also found in thermodynamics. Once again learn to examine the units associated with such numbers,they tell you a lot.

3. Dec 31, 2003

### Hessam

While on the topic of planck... i'm new at physics (self-evidently once you read my question), what exactly is the value of plancks constant? i've read materials that talk about it, but the actual numerical value is what i dont know, any help will be appreciated

4. Dec 31, 2003

### dlgoff

Planks Constant h=6.626x10^-34 Joule sec.

5. Feb 18, 2004

### PRodQuanta

Yes, what dlgoff said is correct. Max Planck was the founder of quantum physics. He said that energy is not continuous, but comes in small, discrete spurts. The energy on one of those spurts = Planck length.

6. Feb 19, 2004

### chroot

Staff Emeritus
Energy and length are of different units.

- Warren

7. Feb 23, 2004

### PRodQuanta

yep, sorry, he's right, and that is what I intended. i meant energy.

8. Feb 24, 2004

### Michael F. Dmitriyev

Any "fundamental constant” is a patch hiding the gaping hole in our knowledge. For example,
gravity force = G*m1*m2/r^2

Presence of G means, that we know nothing about mass, space and gravity. In other cases also.
Any relation should be straight and should not contain any constants.

9. Feb 24, 2004

### Integral

Staff Emeritus
Please ignore the above post, it adds nothing of significance to the conversation.

Boltzmann constant defines the relationship between Temperature and how entropy changes with a changing energy. Bet that helped a lot! Mathematically (which, most likely, will not help much either!)

$$\frac 1 \tau = (\frac {\partial \sigma} {\partial U})_{N,V}$$
Where:
$$\tau = {Fundamental\ Temperature}$$
$$\sigma = {Fundamental\ Entropy}$$
$$U = {Energy}$$

The Boltzmann's constant is defined to be

$$\tau = k_B T$$
Where T is a temperature scale that you are familiar with (Kelvin, Celsius, Fahrenheit etc) depending on the value of kB

this constant is used extensively in thermodynamics.

R the gas constant is defined to be

R = N0kB

N0= 6.022 x 1023
kB=1.38 x 10-18erg/deg
R=8.314 x 107erg/(mole deg)

Always include units with fundamental constants, also to learn about the constant, look at the units. In Physics and chemistry it is essential that you learn to appreciate the physical units attached to a number.

Last edited: Feb 24, 2004
10. Feb 24, 2004

### ahrkron

Staff Emeritus
Re: Re: Numbers and Constants

I strongly disagree with this. Whe you find a relation like that of gravity, you have pretty much nailed down: 1. which quantities are relevant for the interaction, 2. how they are involved in the phenomenon under study, and 3. the fact that a combination of them gives you always the same quantity (G in this case).

Also, constants have to do with the definition of the units you choose to use. Some constants in nature are indeed intriguing (maybe 26), but apart from those, they are not "gaps".