Are Kirchoffs Law and Ohms Law interchangeable?

[eHunter]

Some people feel that Ohm's Law is E= I R, while others say thatis just the definition of R and Ohm's Law is the statement that approximately, and for some materials, R is a constant.

I am of the opinion that Ohm's law can be all of the above since it exhibits commutative, associative and distributive properties and can be sliced, diced and reordered as required to solve an equation.
As to the definition of R, it establishes the relationship of resistance to current and voltage which could be construed as making R a relative constant.

 

[kwired]

Kirchoff and Ohm are two tools, like a slotted and a Phillips screwdriver. There are screws that you can deal with only with one or the other, some that are merely easier with one than with the other, and some where you can use either with equal effort. To be effective in dealing with screws in general you need them both in your toolbox.

Then along comes tamper resistant screws:happyyes:

 

[mivey]

Then along comes tamper resistant screws:happyyes:

At first I had a 25 bit set. Then I get a 100 bit set. What's next?

 

[ggunn]

At first I had a 25 bit set. Then I get a 100 bit set. What's next?

Eventually you will need a cutting torch.

 

[Strathead]

I am confused about this whole discussion. IMO, it started with a nonsensical question and proceeded from there. In the context questioned, you don't use Ohm's law or Kirchoff's law, they just are. Ohm discovered a law regarding the relationship between voltage, amperage, wattage and resistance in a conductor, Kirchoff discovered a relationship of voltage amperage between resistances in a circuit. The law as are then represented by formulas that assign numeric values to those relationships.

 

[gar]

130726-2110 EDT

Strathead:

Power is not part of Ohm's law. That was left to be developed by Joule. This idea that power is part of Ohm's law should not be propagated. It just muddies the water.


To others:

Ohm's law is provable on its own without any knowledge of Kirchhoff's laws.
Kirchhoff's laws are provable without any knowledge of Ohm's law. The two sets of laws cover different subjects. These are not dependent on each other. Ammeters and voltmeters are all that are needed to prove these laws.

Connect a battery, a resistor, and a forward biased diode in series for forward conduction of the diode. Kirchhoff's laws apply. Ohm's law does not apply to the diode, other than for incremental modulated current flow. For gross changes in current thru the diode you can not predict from Ohm's law what the diode voltage drop will be for some other current.

For some incomplete and misleading references see the following:
http://en.wikipedia.org/wiki/History_of_electromagnetic_theory ....... seems like a fairly nice historical reference
See "Early 19th Century"
　
"In 1800 Alessandro Volta constructed the first device to produce a large electric current, later known as the electric battery." ----
"Somewhat important to note, it was not until many years after the discovery of the voltaic pile that the sameness of annual and frictional electricity with voltaic electricity was clearly recognized and demonstrated. Thus as late as January 1833 we find Faraday writing[55] in a paper on the electricity of the electric ray. "After an examination of the experiments of Walsh,[56]HYPERLINK \l "cite_note-57"[57]Ingenhousz, Henry Cavendish, Sir H. Davy, and Dr. Davy, no doubt remains on my mind as to the identity of the electricity of the torpedo with common (frictional) and voltaic electricity; and I presume that so little will remain on the mind of others as to justify my refraining from entering at length into the philosophical proof of that identity." ----
"It is proper to state, however, that prior to Faraday's time the similarity of electricity derived from different sources was more than suspected. Thus, William Hyde Wollaston,[58] wrote in 1801:[59] "This similarity in the means by which both electricity and galvanism (voltaic electricity) appear to be excited in addition to the resemblance that has been traced between their effects shows that they are both essentially the same and confirm an opinion that has already been advanced by others, that all the differences discoverable in the effects of the latter may be owing to its being less intense, but produced in much larger quantity." In the same paper Wollaston describes certain experiments in which he uses very fine wire in a solution of sulphate of copper through which he passed electric currents from an electric machine. This is interesting in connection with the later day use of almost similarly arranged fine wires in electrolytic receivers in wireless, or radio-telegraphy.[13]"
1822 the galvanometer is invented.
This is the state of knowledge and understanding in 1826. As late as 1879 and beyond voltage was referred to as "pressure". The volt had not yet been defined in 1826. Many of the references on Ohm's discovery and experimental proof define the equation in terms of R (resistance). I believe this is incorrect and that the equation was defined in terms of conductivity. Apparently Ohm used a thermocouple as a voltage source because it was more stable. Had a lower internal resistance (today's words and understanding). I have not read Ohm's original work. Galvanometers of that day were not linear. How did Ohm calibrate it for current, and how was it used to measure current? I do not believe the concept of a shunt for measurement of current had been developed in 1879, but it is obvious today.
Many of these authors on history of electrical knowledge are using today's terms and not those of the age being described. Nor adequately describing the experiments and what was done to minimize errors.
I believe that Kirchhoff reformulated Ohm's law from conductivity to resistance. But that does not really change Ohm's law.
http://www-history.mcs.st-and.ac.uk/Biographies/Ohm.html
http://www-history.mcs.st-and.ac.uk/Biographies/Ohm.html
Ohm's name for voltage was electroscopic force
　

 

[mivey]

Ohm's name for voltage was electroscopic force

Then what would he use for units? I kinda like ESFUs. Wouldn't you like to write something like: "We observed that the electroscopic force peaked at 160.7 electroscopic force units"?

 

[ggunn]

Quote Originally Posted by gar View Post
Ohm's name for voltage was electroscopic force

I thought it was electromotive force, or EMF.

 

[Besoeker]

130726-2110 EDT


To others:

Ohm's law is provable on its own without any knowledge of Kirchhoff's laws.

Proved or verified?

 

[gar]

130729-1456 EDT

Besoeker:

Verified is possibly a better word, but Webster's on-line dictionary provides these definitions:

http://www.merriam-webster.com/dictionary/prove

1
archaic : to learn or find out by experience
2
a : to test the truth, validity, or genuineness of <the exception proves the rule> <prove a will at probate>
b : to test the worth or quality of; specifically : to compare against a standard ?sometimes used with up or out
c : to check the correctness of (as an arithmetic result)

3
a : to establish the existence, truth, or validity of (as by evidence or logic) <prove a theorem> <the charges were never proved in court>
b : to demonstrate as having a particular quality or worth <the vaccine has been proven effective after years of tests> <proved herself a great actress>

These definitions certainly include experimental verification.

This forum website has worse problems than last week. Now if you do a Preview Post the original is wiped out, and copying what is in the preview does not return everything. Whatever was done this weekend has not corrected any of the problems generated over the last couple of years.

.

 

[gar]

130729-1512 EDT

ggunn:

http://encyclopedia.thefreedictionary.com/Electroscopic
http://books.google.com/books?id=-c...onepage&q=electroscopic force and ohm&f=false
http://www.science20.com/chatter_box/genius_georg_ohm-86122 useful but does not use original terms

All of the above essentially translate into the modren form of Ohm's law.
The original book or discussion is found in
Die galvanische Kette, mathematisch bearbeitet 1827 and obviously in German.

There may be an English translation in Taylor's Scientific Memoirs 2 of 1841. This reference appears in Google references, but the book itself does not pop up. There is apparently a reprint at the U of M library.

The above references that claim to describe what Ohm originally did take too much liberty in their description. Thus, you can not get a clear understanding of how the subject was addressed in 1825-1827. It seems that Ohm was the first to try to apply a mathematical approach to the study of electrical circuit theory. Really the properties of conduction. Prior researchers assumed that there was not sufficient consistency or repeatability to apply math to the subject. Discussions were very qualitative.

I believe EMF was not a term of 1825 or 1827.

As I have stated before, good instrumentation was not created before Edison's work of 1879. It was the mid 1880s before Weston produced a practical volt or ammeter. Non-linear galvanometers, potentiometers, batteries, standard resistors, and Wheatstone bridges were the only precision components prior to 1879. But some of these were not precision in terms of what we consider precision today. In particular resistors and batteries. The galvanometer was a good null indicating device, but not precision in other respects.

.

 

[gar]

130729-2148 EDT

Now I have found a reference in English that describes Ohm's experimental setup. This clears up how accurate current measurements were made, and how voltage was adjusted. But does not clarify names like EMF, volt, resistance, and conductance.

Basically current was measured by a force null balance method. This eliminated the non-linearity deflection problem of a galvanometer.

See pages 227 thru 232 at least in
http://books.google.com/books?id=ICASAAAAYAAJ&pg=PA219&dq="seat+of"+"electromotive+force"&hl=en#v=onepage&q="seat of" "electromotive force"&f=false
"A History of Physics in Its Elementary Branches", by Florian Cajori.

.

 

[Besoeker]

130729-1456 EDT

Besoeker:

Verified is possibly a better word, but Webster's on-line dictionary provides these definitions:

I know I have probably related this before.
When I was at secondary school (it's usually age 11 to 16 in UK) we had what I came to realise was an excellent physics teacher.
I don't exactly remember what age I was but probably around fifteen.

"Class, what are we going to do today?"
"Prove Ohm's Law" I suggested.
He gave me a steely gaze.
"No we are not." In measured tones.
"We may verify it."
Over half a century ago but it has stuck with me.

 

[mivey]

I know I have probably related this before.
When I was at secondary school (it's usually age 11 to 16 in UK) we had what I came to realise was an excellent physics teacher.
I don't exactly remember what age I was but probably around fifteen.

"Class, what are we going to do today?"
"Prove Ohm's Law" I suggested.
He gave me a steely gaze.
"No we are not." In measured tones.
"We may verify it."
Over half a century ago but it has stuck with me.

15? Why didn't you just go ask Ohm?

 

[Besoeker]

15? Why didn't you just go ask Ohm?

What makes you think I didn't?

 

[Sahib]

I know I have probably related this before.
When I was at secondary school (it's usually age 11 to 16 in UK) we had what I came to realise was an excellent physics teacher.
I don't exactly remember what age I was but probably around fifteen.

"Class, what are we going to do today?"
"Prove Ohm's Law" I suggested.
He gave me a steely gaze.
"No we are not." In measured tones.
"We may verify it."
Over half a century ago but it has stuck with me.

The Physics teacher probably stressed verification of ohm's law, because it was, perhaps, an experiment class that day. In fact, the ohm's law can be proved from theoretical considerations.

Over half a century of ignorance busted.

 

[JDBrown]

Over half a century of ignorance busted.

Wow. Of the many things one could call Besoeker, "ignorant" is not one I would pick. Why the arrogance and animosity, Sahib? It's obvious that he wasn't suggesting that Ohm's Law can't be proved, just that it can't be proved by taking measurements of a physical circuit--only verified.

Ironically, you're ridiculing the man for saying essentially the same thing you did. The only difference is that he said it over a week ago (and he was polite about it).

 

[Sahib]

Wow. Of the many things one could call Besoeker, "ignorant" is not one I would pick. Why the arrogance and animosity, Sahib? It's obvious that he wasn't suggesting that Ohm's Law can't be proved, just that it can't be proved by taking measurements of a physical circuit--only verified.

Ironically, you're ridiculing the man for saying essentially the same thing you did. The only difference is that he said it over a week ago (and he was polite about it).

Nothing like that intended.

Ohm's law was not, at first, understood or accepted by the scientific community for a very long time.

Only after a theoretical consideration of the law by the Royal Society of England, the law was finally accepted.

I stated in that context.

 

[Sahib]

Wow. Of the many things one could call Besoeker, "ignorant" is not one I would pick.

Neither do I.

Why the arrogance and animosity, Sahib?

This is ridiculous. Discussion per forum rules.

It's obvious that he wasn't suggesting that Ohm's Law can't be proved,

It's obvious that he implied it.

just that it can't be proved by taking measurements of a physical circuit--only verified.

Only you are stating it. Blind support.

Ironically, you're ridiculing the man for saying essentially the same thing you did. .

He did not.

 

[Besoeker]

Nothing like that intended.

Me :Over half a century ago but it has stuck with me.
You: Over half a century of ignorance busted.

Difficult to see that as anything other than intentionally offensive and specifically directed at me.
Given your other posts in perfectly good English, it cannot be excused on language differences.
The gentlemanly thing to do would be to retract the statement.
But, water under the bridge. What was said was said.

My point was about verification, not proof.