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UK back to "imperial" measurements ?
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mclute0:
So just for fun, and in the spirit of inclusivity and human/universe coexistence, I think we need some new standards of measurement that are universal and not based on human truths.

Why do I say this? I really like the Asimovian idea that at some point, maybe a megaannum from today, we will meet other intelligences and if out systems are based on universal truths our ability to communicate will be much improved.

What do I mean by universal? I would perhaps start with say the wavelength of the first spectral line of Lyman series for Hydrogen as the base unit of measurement of distance.

Is that the best we could do? Probably not, but it gives you the idea. What we call the measurements is not nearly important as the understanding of their context. Like using base 2 with computers and not human centric base 10, adapting to a new system is only more mathematics, but using that new system improves the related system of communication.

Just hope we don't meet the Mule.

I wonder if Asimov would have done TikTok.

All your Tide Pod are belong to us!

free_electron:

--- Quote from: magic on May 30, 2022, 09:01:55 am ---So the new unit of voltage is pound times square inch per coulomb per square second? I will try to remember ;D
Is there an imperial unit of charge I forgot about?

--- End quote ---
seconds need to be defined in fractions of fortnights...
TimFox:
There is a "customary" unit for magnetic flux density (B-field):  lines/in2.
1 line/in2 = 15.5 uT.
(The "line" corresponds to the old cgs unit "Maxwell" or Mx)
In older electrical engineering, one can find "Mx/in2" and "Wb/in2".
In modern SI, 1 T = 1 Wb/m2 is the preferred name for magnetic flux density or "magnetic induction" B.
In rationalized units, the other field H in A/m is called the "magnetic field", just to confuse people.
IanB:

--- Quote from: TimFox on June 02, 2022, 07:12:00 pm ---In rationalized units, the other field H in A/m is called the "magnetic field", just to confuse people.

--- End quote ---

If I envisage a long, thin, straight conductor in free space, and I want to consider the magnetic field strength in the proximity of that wire, then the only two considerations are the current in the wire, and the distance from the wire. The magnetic field increases with current, and is presumably proportional to the current, so it is "A times something". The magnetic field decreases with distance from the wire, so we will be dividing by distance. At the simplest we therefore have "A/m".

What is the intuition that tells is it is A/m rather than, say, A/m2 ?

The best I have is that the inverse square law typically applies to distance from a point source (zero dimensions). Since in our case we have a long straight wire (one dimension instead of zero dimensions), the inverse square law loses a dimension and becomes a simple inverse.
TimFox:
That's as good an "intuitive" explanation as any.  Another explanation is that if you do a line integral of H along a closed curve, it equals the total current (in Amp-turns) crossing the 2D surface enclosed by the curve.
In electromagnet design, H is often measured in "Amp-turns/meter" for that reason.
The difference between "rationalized" units, including modern SI, and "unrationalized" units, such as "Gaussian" cgs is where to put the 4 pi in the equations.
In Gaussian units (preferred by some physicists who don't own Simpson 260 meters), B and H are in the same units (Gauss), although H is sometimes called out as "Oersteds", even though that equals the Gauss.
In "rationalized mks" (SI) units, they are related in vacuum by B = (4pi)x10-7 x H, where the factor (permeability of free space) is an exact constant that defines the Ampere through the other equations.
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