How is it [Ohm's Law] stated exactly?
A physics textbook by Halliday,Resnick that is used in colleges and has been translated to different languages, clearly says that the relationship V=RI is not a statement of Ohm's law and a conductor obeys Ohm's law only if its I/V plot is linear or, in other words, if R is constant.
The authors also say that the relationship R=V/I remains as the general definition of the resistance of any device. ohms = volts / amperes with no other implications; you can always measure a voltage and a current through a device, calculate their ratio and say that it is a resistance.
That's about as definitive a statement for Ohm's Law that has been
presented so far, and if i could i would quote it about 20 more times.
Thanks for the post eng, i wish you were here for the start of this
debate.
Key points:
1. V=RI is *not* a statement of Ohm's Law.
2. Obeys Ohm's Law only if R is constant.
To me, this is self evident because we would not have any rule about
anything if in fact it did not do anything. Also, we can not take the
stand that "any R in real life is not constant" because that is not how
we develop theoretical laws and formulas...if we did we wouldnt have
any laws because nothing behaves like its law says it does except
within some bounds of some kind. Theory comes before practicality.
We *apply* the theory to the practical case and accept some small
inaccuracies sometimes even though we dont explicitly define them.
If we did try to get perfect answers every time we would have to
reject all calculations done for anything we know of in real life.
A duck is a duck is a duck is a duck, but that's for more casual
conversation, not for a technically oriented debate where the
species comes into question. I had many types of fish in my life
and i learned the species of all of them. When i am talking to the
neighbor about fish it might be ok to just call them 'fish', but when
talking to experts in the field it makes the conversation more intelligent
to include the species.
So part of the background of how we talk about things in general is
who we are talking with, and here, in this thread, we are talking with
experts and we want expert opinion, not just casual conversation.
This is partly so we can convey the best possible information to the
newcomers in the field.
Sceadwian, i sympathize with you because, of all reasons, i once took
your view about this too. I have since learned the better view after
taking a wider perspective on what any rule is in general and doing
tons of lab work.
PS
The little cartoon was quite funny A nice addition if you ask me.
Last edited: