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-MFra-21-Topaz II
21-Topaz II
May 25, 2017
Solved

Rydberg's constant in mathcad 15 is wrong

  • May 25, 2017
  • 4 replies
  • 5694 views

The universal constant R is incorrect in mathcad 15. Is it so for you too?

Rydbergs constant.jpg

Best answer by LucMeekes

Presently the speed of light is defined as (exactly!): and

the unperturbed ground state hyperfine transition frequency of the caesium 133 atom is (exactly):

As of (sometime) next year (see http://www.bipm.org/utils/common/pdf/si-brochure-draft-2016b.pdf)

the following definitions will apply (and they will all be exact; their final exact values need to be determined, but they will be close to):

Plank constant:

Electron charge:

Boltzmann constant:

Avogadro constant:

The luminous efficacy Kcd of monochromatic radiation of frequency 540 ×10^12 hertz:

Further is determined (not exact):

With those, other natural constants become:

Luc

4 replies

L
LucMeekes23-Emerald IV
23-Emerald IV
May 25, 2017

With R you probably have hit the Rankine temperature unit defined in Mathcad 15. The Rankine scale starts at absolute 0 (that is 0 K) and steps in units of the Fahrenheit scale..

So Rankine relates to Fahrenheit as Kelvin relates to Celsius.

The Rydberg constant is written and known as follows:

The value commonly denoted with R, and that has a value of about 8.314, is the Universal gas constant:

Success!
Luc

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-MFra-21-Topaz IIAuthor
21-Topaz II
May 25, 2017

I apologize, I did some confusion ...

universal constants.jpg

I would be very grateful if you find any imperfections in the previous list. Thank you very much

L
LucMeekes23-Emerald IVAnswer
23-Emerald IV
May 25, 2017

Presently the speed of light is defined as (exactly!): and

the unperturbed ground state hyperfine transition frequency of the caesium 133 atom is (exactly):

As of (sometime) next year (see http://www.bipm.org/utils/common/pdf/si-brochure-draft-2016b.pdf)

the following definitions will apply (and they will all be exact; their final exact values need to be determined, but they will be close to):

Plank constant:

Electron charge:

Boltzmann constant:

Avogadro constant:

The luminous efficacy Kcd of monochromatic radiation of frequency 540 ×10^12 hertz:

Further is determined (not exact):

With those, other natural constants become:

Luc

M
mvenich14-Alexandrite
14-Alexandrite
May 25, 2017

In Mathcad 15, R is a Rankine (unit of temperature that's equal to 5/9 Kelvin)

In Mathcad Prime 4, R can mean Rydbergs constant or the universal gas constant ( I don't think Prime knows Rankine temperature units)

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-MFra-21-Topaz IIAuthor
21-Topaz II
May 25, 2017

I apologize, I did some confusion ...

F
Fred_Kohlhepp23-Emerald I
23-Emerald I
May 25, 2017

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-MFra-21-Topaz IIAuthor
21-Topaz II
May 25, 2017

I mistakenly called the perfect gas constant, R, with the name of another constant, that is, Rydberg. Also, while Prime supplies the correct R value (constant of perfect gases) (written with the label constant). This does not happen in mathcad 15, ie when writing R = mathcad provides a temperature.

D
DJF16-Pearl
16-Pearl
May 25, 2017

So I'd never noticed R was built-in before this thread, and had always defined it myself.  So I did a little comparison and found something interesting. The mathcad (Prime 3.1) R value does not appear to be correct. 

2017-05-25_16-20-34.jpg

L
LucMeekes23-Emerald IV
23-Emerald IV
May 25, 2017

That's the problem with many of those natural constants. They change all the time.

Fortunately we'll be rid of many of that sometime next year. Then R (gas constant) will be exactly known.

It's a good thing you always defined R yourself.

Luc

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