Ohm's law is the definition of the relationship of previously defined units of current, voltage, resistance and power.
Ed and John occasionally mistake non-linear resistance (or TC for that matter) with violation of Ohm's Law. Nothing restricts resistance to be invariant with any other parameter.
I still can't convince myself that the source's current output, or even noise, is relevent to the issue of base current injection, unless somehow *all* of the source's current could be injected and become charge carriers.
But the integral carrier injection, that you refer to in your second point, is the part that is (even further) over my head. Is it a fact that charge injection is quantized to one electron size? If so then the effect would seem to fall out naturally, like shot noise, (however small it may be).
Thanks,
Chris
There are two 'Ohm's Laws', one has been refuted by new and different research of the human ear. Many here think that a 'Law' was written in stone or something. Often, people rigidly keep to these 'Laws' as if they were an addition to the 10 Commandments or something. This keeps people thinking 'inside a box'. Difficult to do anything 'extra special' staying in that mode. Might give someone a raise at their company for being a 'good soldier' however, for not making 'waves' by trying something new and 'radical'. Very corporate.
Agreed. When I learned Ohms law power was not a consideration
(nor for sure part of the equation)
Maybe Watt delveloped I^2 / R
For those who may not know but are interested in the application of Ohm’s law as it applies to fundamental quantities and measurements today–
The quantity for resistance as we know it today is represented by a fundamental physical process, the quantum hall effect. We have Klaus von Klitzing to thank for this circa 1980. The quantity for voltage is currently derived from a near perfect frequency-to-voltage converter based on another fundamental process of physics that grew out of the theoretical work of Brian David Josephson (he also has some interesting views on complex systems, biology, and their relation to physics). The frequency reference for this frequency-to-voltage converter is based on yet another fundamental physical constant, the molecular electronic transition of Cesium-133.
Here is the ironic part - BIPM (the international standards body responsible for defining the quantities to which measurements everywhere on this planet relate) defines the value assigned to the Von Klitzing and Josephson constants as derived from measurements using the international kilogram. This “standard” for the physical quantity of mass is not based on a fundamental physical process but on an artifact standard created as one of two prototypes in 1889. http://www.bipm.org/en/scientific/mass/pictures_mass/prototype.html It is very slowly, and somewhat mysteriously, losing weight over time. Work is under way to replace it with a quantity based on a physical constant or quantity in the future.
More to the point, the ampere SI base unit is “best realized through combinations of realizations of the watt, the ohm and the volt”. So today the kilogram, power, and ohms law best represent the volt and ohm, not the other way around…
Dave
BIPM - SI
When you trace all these 'fundamental' definitions through to the end, you'll find that more and more are ultimately being based on units of 'things per unit of time'.
jan
No. Ohm's 'law' is an observation of the electrical behaviour of many, but certainly not all, conductors. It is only true for ohmic conductors i.e. conductors for which it is true. If it were a law of nature it would be true for all conductors.Joshua_G said:
No! That is precisely the (opposite of) the point I was making. F=ma is true for all classical bodies - no exceptions. It is a law of nature. V=IR is only true for those conductors and voltages/current for which it is true. Even an ordinary resistor is only ohmic over a limited range, and all the debates about resistor distortion show that even then it is only a good approximation.vacuphile said:
As it stands this sentence is nonsense, so I can only assume John meant it in some meta-physical sense which eludes me.john curl said:
Let's learn some elementary EE:
Kirchoff's laws are laws of nature, being based on charge conservation and the conservative nature of the static electric field (so we can define potential difference).
P=IV is a law of nature, as it comes from integrating the Ponting vector over a closed surface.
V=IR is not a law of nature, but an observation of the approximate linearity of many conductors. That is all.
Everyone (educated) knows that. It does not mean that the equation is not valid for an idealized abstract model.
Yes, of course. I didn't want to introduce vector field theory into the discussion, as it doesn't change the point and might go over some peoples' heads. The basic point, which still seems not to be fully accepted, is that linear resistance is an approximate property of some materials not a property of the universe. On the other hand, conservation of charge (for example) from which we get Kirchoff's current law is a property of the universe, not just a property of electrons. If we could build circuits using muonics or positronics we would still use Kirchoff's current law.
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