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

Rydberg's constant in mathcad 15 is wrong

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

Rydbergs constant.jpg

LucMeekesAnswer
23-Emerald V
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

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10 replies

LucMeekes23-Emerald V
23-Emerald V
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

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LucMeekes23-Emerald VAnswer
23-Emerald V
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

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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 ...

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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.

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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

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LucMeekes23-Emerald V
23-Emerald V
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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