Having said that, let me now define Ohm's Rule:
Any element that has constant R for any v or i follows Ohm's Rule.
The context here is that v and i are allowed to vary, but R is not.
Now, there is no getting away from this fact, that R must be constant, because i had
just declared that if you want it to follow Ohm's Rule then you must insist that
R be constant.
Still havent heard from anyone about who first discovered Ohm's "Law" either.
Ohm's Law.
The electromotive force acting between the extrmeities of any part of a circuit is the product of the strength of the current, and the resistance of that part of the circuit.
Here a new term is introduced, the resistance of a conductor, which is defined to be teh ratio of the electromotive force to the strength of the current which it produces. The introduction of this term would have been of bi scientific value unless Ohm had show, as he did experimentally, that it corresponds to a real physical quantity; that is, that it has a definite value which is altered only when the nature of the conductor is altered.
In the first place, then the resistance of the conductor is independent of the strength of the current flowing through it.
In the second place the resistance is independent of the electrical potential at which the conductor is maintained, and of the density of the distribution of the electricity on the surface of the conductor.
It depends entirely on the nature of the material of which the conductor is composed, the stae of aggregation of it's parts, and it's temperature.
The resistance of a conductor may be measured to within one ten thousandth, or even one hundred thousandth of a part of it's value, and so many conductors have been tested that our assurance of the truth of Ohms's Law is now very high." - Electricity and Magnetism. Maxwell, 1873 vo. i pp 296.297
Mike, from that perspective there is no real world substance that actually obey's Ohm's law, but again it's semantics. Ohm's law was derived from real word tests on conductors at fixed temperatures, he admitted that things were more complex than that but the general equations are so useful it can be gleefully overlooked.
I am not debating on the 'ohm's law' here. I am only referring to V=IR.
Suppose we somehow include the 'resistance' offered by the electric fields inside the diode + all the other resistances + parasitic inductances,capacitances , then wont the diode still follow V=IR at every instantaneous point of time?
Here are my 2 cents on this topic:
I agree with Sceadwian's concept of effective resistance. It makes complete sense. wschroeder said that he demonstrated the concept of inductive reactance by plugging in a roll of copper wire into the mains and having nothing blow up. I'm sure that in 1700s , this behavior , if it had been noticed , would have been branded as a case of disobeying of ohms law. However , now that we know about inductive reactance , we can also include the effects of inductance by adding another (frequency dependent)resistance in our mathematical models.
My point is that , in a semiconductor junction , there are effects of electric fields which may impede/promote current flow. Just like , the definition of resistance was broadened to impedance when inductive reactance was discovered , why dont we change the definition again to include interactions of electric fields on the charge carriers at the microscopic level?
Surely wont that make things easier to analyse?
I am not debating on the 'ohm's law' here. I am only referring to V=IR.
Suppose we somehow include the 'resistance' offered by the electric fields inside the diode + all the other resistances + parasitic inductances,capacitances , then wont the diode still follow V=IR at every instantaneous point of time?
@ericgibbs
If V=IR hold goods for every instantaneous point of time , then whats the problem? Doesnt that imply that semiconductor junctions also obey v=IR?
V=IR no where mentions anything about time at all.
And why does ohms law assume that the only type of resistance is the 'ohmic resistance'? Isnt resistance just anything that impedes current ? So logically , all components that impede current (L.reactance , C.reactance , drift velocity saturation (?) , electric field influence etc..) must be
@ericgibbs , does that imply that diodes indeed do obey ohms law?
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