Did Ohm, Ampere, and Volta Collaborate on Ohm's Law?

[akerkarprashant]

TL;DR

History behind Ohm's law.

Voltage SI unit = Volts
Current SI unit = Ampere
Resistance SI unit = Ohm

Ohm's law : V=IR

Did Georg Ohm (German), Ampere (French) & Volta (Italian) collaborated when Ohm came out with this electricity equation with units for voltage, current & resistance as per their surnames?

Credit goes to all. Volt & Ampere units were already in place?

Ohm came out this electricity equation.

 

[Baluncore]

https://en.wikipedia.org/wiki/Georg_Ohm#Discovery_of_Ohm's_law

Ohm 1827 "The galvanic circuit investigated mathematically".
https://ia802908.us.archive.org/12/..._circuit_investigated_mathematically_text.pdf

 

[DaveE]

 

[glappkaeft]

Credit goes to all. Volt & Ampere units were already in place?

The units where Volt, Ampere and Ohm where defined in the 1870s/early 1880s long after the people they where named for had died.

 

[Meir Achuz]

Ohm seems to have presented Ohm's law before units were introduced.
I believe the first units were the emu units defining the 'absolute ampere' (or abampere ) by
F/L=2II'/d. Does anyone know when, and for what reason, the SI ampere=abampere/10 was introduced.
That is related to when and why the SI ohm was introduced.

 

[Baluncore]

Does anyone know when, and for what reason, the SI ampere=abampere/10 was introduced.
That is related to when and why the SI ohm was introduced.

There was a meeting in Britain over some days in 1861. A discussion over dinner one evening, sorted out which eponym would be associated with which physical parameter. The vote took place and the overnight discussion was reported in a note. I believe that is how the names were allocated to the SI units.
I followed it this far previously.
https://www.physicsforums.com/threa...conductivity-denoted-by-g.974343/post-6214413

 

[akerkarprashant]

Siemens unit

Thanks.

The Conductance unit Siemens named after Ernst and Specific Resistance Mho were named after Ohm?

 

[Meir Achuz]

I'm not interested in the names.
When and why was the abampere changed to the ampere so that we have 30 amp fuses and not 3 abampere fuses (if anyone remembers what a fuse is)?

 

[Baluncore]

... Specific Resistance Mho were named after Ohm?

The "mho" is simply "ohm" spelled backwards to signify the reciprocal.
Mho was a widely used informal conductance unit equal to inverse resistance.

For a while in the 1930s there was a reciprocal to the farad of capacitance. Reciprocal capacitance was called "elastance", and the unit "daraf" was also derived from a backward spelling.

https://en.wikipedia.org/wiki/Elastance#Units

 

[Baluncore]

I'm not interested in the names.

You may not be, but other members are.

When and why was the abampere changed to the ampere so that we have 30 amp fuses and not 3 abampere fuses (if anyone remembers what a fuse is)?

The abampere was part of the cgs system that was replaced by MKSA in the 1960s.
https://en.wikipedia.org/wiki/Abampere

The original "Georgi system" became MKSA, which became SI.
https://en.wikipedia.org/wiki/Giovanni_Giorgi#The_Giorgi_system

 

[Meir Achuz]

I'm afraid my question is still misunderstood. I know about the convention in 1960.
I am asking about the history from Wikipedia:
"an international convention, signed at the 1881 International Exposition of Electricity, established the ampere as a standard unit of electrical measurement for electric current.
The ampere was originally defined as one tenth of the unit of electric current in the centimetre–gram–second system of units." The Ampere must have been in some use before that, and why wasn't it made equal?

 

[vanhees71]

Maybe this answers part of your question. I'm always glad when I get the confusing SI units right in my intro-E&M lecture ;-)).

https://www.iec.ch/history-si

 

[bob012345]

So you're saying Ohm met a lot of resistance when he proposed his law...

 

[Orthoceras]

I believe the first units were the emu units defining the 'absolute ampere' (or abampere ) by
F/L=2II'/d. Does anyone know when, and for what reason, the SI ampere=abampere/10 was introduced.
That is related to when and why the SI ohm was introduced.

I'm afraid my question is still misunderstood. I know about the convention in 1960.
I am asking about the history from Wikipedia:
"an international convention, signed at the 1881 International Exposition of Electricity, established the ampere as a standard unit of electrical measurement for electric current.
The ampere was originally defined as one tenth of the unit of electric current in the centimetre–gram–second system of units." The Ampere must have been in some use before that, and why wasn't it made equal?

In 1862 the British Association chose, in a report, the practical units for voltage and resistance: 1 volt = 10^8 emu ('electromagnetic unit') of emf, and 1 ohm = 10^9 emu of resistance. The practical unit for current remained unnamed, but in 1875 it got the temporary name weber, and in 1881 it was renamed to ampere. The ampere was defined as 1 volt / 1 ohm.

The sizes of the emu of emf and the emu of resistance were inconveniently small for practical purposes. The size of the emu of current was not inconvenient, but the inconvenience was that is was not coherent with the practical units volt and ohm. (The name abampere did not yet exist, until 1904.)

 

[Meir Achuz]

The history in https://www.iec.ch/history-si explains a lot, but still leaves me with some questions.
Its seems that the ohm was chosen in 1881 so that "The ampere was originally defined as one tenth of the unit of electric current in the centimetre–gram–second system of units." (Wikipedia). The column of mercury was just the length for that. Would it have been that inconvenient to designate that measured resistance as 0.1 ohm? Were there already two Amperes before 1881? If they called the measurement 0.1 ohm, there would be only one ampere, and SI units would be the rationalized emu system. That would make it easier to "get the confusing SI units right."

 

[Baluncore]

The column of mercury was just the length for that.

The length and diameter of the mercury column was chosen to give that resistance, so the standard could be regenerated elsewhere.

Were there already two Amperes before 1881?

You need to work in one system only at one time. CGS or MKS, don't try to mix the systems.

 

[vanhees71]

The history in https://www.iec.ch/history-si explains a lot, but still leaves me with some questions.
Its seems that the ohm was chosen in 1881 so that "The ampere was originally defined as one tenth of the unit of electric current in the centimetre–gram–second system of units." (Wikipedia). The column of mercury was just the length for that. Would it have been that inconvenient to designate that measured resistance as 0.1 ohm? Were there already two Amperes before 1881? If they called the measurement 0.1 ohm, there would be only one ampere, and SI units would be the rationalized emu system. That would make it easier to "get the confusing SI units right."

I was more referring to the idiosyncratic definition of $\mu_0$ and $\epsilon_0$ and the fact that they choose the components of the electromagntic field $(\vec{E},\vec{B})$ to have different dimensions. From a physical point of view it's very confusing. Overall there were many systems of units in use like electrostatic, magnetostatic, Gaussian, rationalized Gaussian (aka Heaviside-Lorentz). The latter are the physically most adequate ones, but from a practical point of view unhandy.

 

[Meir Achuz]

I understand that muzero is now to be measured experimentally. I used to use that as a joke.

 

[vanhees71]

Well, the "new SI" is indeed a big progress from a metrological point of view. Since now the elementary charge $e$ is fixed by definition, $\mu_0$ is now to be determined empirically. Together with the defined value of $c$ (speed of light in vacuo) then $\epsilon_0$ is also determined.

 

[Vanadium 50]

I understand that muzero is now to be measured experimentally

Yes. 4π is now a measured number.

 

[Klystron]

Maybe this answers part of your question. I'm always glad when I get the confusing SI units right in my intro-E&M lecture ;-)).

https://www.iec.ch/history-si

I told my beginner EM classes that unit assignment was an 'evolving process'. Students appreciated ohm and mho as reciprocal units for resistance and conductance. A 'light would go on' and students would exclaim, "Now I get it!".

Perhaps the family name siemens was more well known in Europe. I invariably invert the 'i' and 'e'.

Weber also enjoyed lingering minor affection as the name appeared on useful tools. I cannot remember an American ever saying ampere outside a lecture hall, but monosyllabic amp became ubiquitous and very popular.

"I was so amped by your lecture!".