| Re: Physical constants in IDL with !CONST [message #82580 is a reply to message #82525] |
Thu, 20 December 2012 11:10   |
chris_torrence@NOSPAM
Messages: 528
Registered: March 2007
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Senior Member |
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On Thursday, December 20, 2012 10:36:21 AM UTC-7, Heinz Stege wrote:
> On Thu, 20 Dec 2012 06:24:31 -0800 (PST), wlandsman wrote:
>
>
>
>> I wonder if the constants should be !DtoR and !RtoD (or RADEG and DEGRA) to correct the earlier inconsistency in the ancient history of IDL. I'm not sure about this, though. --Wayne
>
>>
>
> A lot of discussions for a little thing, that everyone can do her or
>
> himself within a startup file.
>
>
>
> However, I think Wayne is absolutly right.
>
>
>
> A similar point is, that I wouldn't name the elementary charge "eV". I
>
> know, there is a name conflict with the Euler's number. However the
>
> Euler's number can simply be calculated by number=exp(1d). Therfore I
>
> suggest to simply remove it from the table.
>
>
>
> Please realize, that most of the "constants" are from physics and
>
> chemistry and the Euler's number is a mathematical number which never
>
> will change. (You may argue, that pi also is a mathematical constant,
>
> however it is needed [even though by definition] for the calculation
>
> of the magnetic constant mu0=4d*!dpi*1d-7)
>
>
>
> The name "ev" for the elementary charge is confusing, because the
>
> definition of the elementary charge constant has nothing to do with
>
> the energy unit "electron volt". The reason for 1 eV being 1.602...
>
> 10^-19 J only reflects, that changing the potential of a charge e
>
> about 1 V means an energy change of 1.602... 10^-19 J.
>
>
>
> Thats what I wanted to say.
>
>
>
> Cheers, Heinz
On Thursday, December 20, 2012 10:36:21 AM UTC-7, Heinz Stege wrote:
> On Thu, 20 Dec 2012 06:24:31 -0800 (PST), wlandsman wrote:
>
>
>
>> I wonder if the constants should be !DtoR and !RtoD (or RADEG and DEGRA) to correct the earlier inconsistency in the ancient history of IDL. I'm not sure about this, though. --Wayne
>
>>
>
> A lot of discussions for a little thing, that everyone can do her or
>
> himself within a startup file.
>
>
>
> However, I think Wayne is absolutly right.
>
>
>
> A similar point is, that I wouldn't name the elementary charge "eV". I
>
> know, there is a name conflict with the Euler's number. However the
>
> Euler's number can simply be calculated by number=exp(1d). Therfore I
>
> suggest to simply remove it from the table.
>
>
>
> Please realize, that most of the "constants" are from physics and
>
> chemistry and the Euler's number is a mathematical number which never
>
> will change. (You may argue, that pi also is a mathematical constant,
>
> however it is needed [even though by definition] for the calculation
>
> of the magnetic constant mu0=4d*!dpi*1d-7)
>
>
>
> The name "ev" for the elementary charge is confusing, because the
>
> definition of the elementary charge constant has nothing to do with
>
> the energy unit "electron volt". The reason for 1 eV being 1.602...
>
> 10^-19 J only reflects, that changing the potential of a charge e
>
> about 1 V means an energy change of 1.602... 10^-19 J.
>
>
>
> Thats what I wanted to say.
>
>
>
> Cheers, Heinz
Hi Heinz,
That's a really good point. I had the same dilemma about "eV" when I put it in. I like your idea of getting rid of "e".
Also, yes, I'll make the "DtoR" and "RtoD" consistent. Maybe "DegRad" and "RadDeg", so at least they are somewhat human-readable?
-Chris
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