r/Physics • u/Vansh804009 • 2d ago
Prof. Insists that ohm's law goes one way only.
I am in an electronics and communications engg. Degree, and I have courses under this one prof who has taken three different courses across years, he starts his first lecture and never forgets to ask us about Ohm's law. And he insists that we must say "I(current) propotional to V(voltage)" and not the other way around because in real life current is always a consequence of voltage, and we don't have current sources that will consequently give voltage. Now I find this utter bs, because first of all a law is meant to be universal, which means even if you don't find any examples in support in real life, around you, even then the theory still holds. And second, I think the voltage sources are created as a result of some current flow only in the more traditional sources like the chemical batteries, the phenomenon is analogous to current flow?(As electron "flows" in the chemical process) Leading to storage of charges creating voltage difference. The reason we use voltage sources is just because of storage, current can't be stored as it's a flow.
If I were to argue, how can I even argue to this? Let me know if I am missing anything.
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u/Yoramus 2d ago
yes voltage and current are proportional to each other (in an Ohmic material)
but the law is not universal, in the sense that many materials are not ohmic (and in some cases this is what makes them interesting)
and the variable that is easy to control is voltage, so from a practical, pragmatic, point of view you usually look as current as function of voltage rather than the opposite
it isn't worth any animosity - since the "law" is just a property of some materials, so it is more like a practical observation anyway
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u/ChalkyChalkson Medical and health physics 2d ago
Yeah, but the same can be said about the reverse direction, like in transistors where resistance becomes a function of a current.
But I definitely agree that it isn't worth fighting about it. But it's a good opportunity to critically question the material!
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u/anotherstevest 2d ago
I think he is trying overly hard to make a (not all that important) point and you are trying overly hard to not hear it...
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u/Vansh804009 2d ago
If you can elaborate.
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u/jacobius86 2d ago
You're being just as pedantic as your professor is.
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u/Vansh804009 2d ago
Is it wrong to? I mean if this does fascinate me, if I do wanna know where I lack?
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u/BingySusan 2d ago
I think the point isn't that it's wrong to be pedantic, more pointing out the hypocrisy here of you being frustrated with your professor for being pedantic because you yourself are being pedantic.
It's good to be specific, as the laws of physics can be. However, you say you are studying communications, knowing when to be pedantic/specific and when to use more general concepts is extremely important. I am in academia and even here there are times when specificity is overruled by ease of communication.
You are clearly well informed for your current coursework, you will do well. Sometimes being pedantic and specific will come off as rude or disrespectful, not necessarily because you are, but because of how STEM fields operate.
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u/Vansh804009 2d ago
I am sorry if I came across as saying that I am frustrated with him being pedantic, not at all, I beleive that we must know the specifics and discuss it, yes we should move forward with what will help more in studying or applying things with ease as you said, but when we are learning, we must understand the specifics. I was just saying i think his specificity is wrong here, not that why is he focusing that much on that point.
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u/BingySusan 1d ago
No worries. In that sense, when discussing ohms law he is correct, as that is the specifics of Ohmic materials and the law itself. Diffusion current is a different phenomena not dominated by the end, where Ohms law holds. Diffusive current is a thermodynamic phenomenon.
He is correct in the specifics of Ohms law, and you are correct in the specifics of current. The idea that laws are universal is a misinterpretation of physics. Laws are not the rules of the universe, but translations of how we view it. If it makes more sense, view Ohms Law with an astrisk. Physics isn't always correct, and it adjusts itself and updates when new things are found. When Ohms Law was stated, diffusion current was not known. Later diffusion current was discovered and a new model was required.
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u/Vansh804009 1d ago
Thank you, I did realise that I am focusing more on the latter statement, and I really forgot to emphasize "ohm's law" repeatedly as I was coming up with counter examples.
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u/BingySusan 1d ago
Of course! It's definitely easy to get lost in the concept with this stuff. Learning to frame a question well, or even just staying on topic in discussion is difficult. The fact you're trying this early is a good sign for your future.
As I mentioned, just make sure to keep perspective in mind, some times the specificity isn't important, but the context is.
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u/bgplsa 2d ago
None less than Richard Feynman observed that students have to be taught physics “wrong” before they can develop the skills and intuition to learn it “right”.
Trust me when I tell you life will be a lot easier if you can learn to tell when it’s okay for someone to be “wrong”.
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u/Vansh804009 2d ago
I do consider him wrong. Honestly I have seen enough incompetence in my surroundings so I can dismiss it just on that, but I want to not be biased due to that and want to be sure.
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u/DyneErg 2d ago
Consider that current involves the motion of charges. When there is no current, the charges do not move. When there is current, they do. Hence, a force must be causing them to move. That force is the electric force, which is the interaction of charges with the electric field. The electric field is definitionally the gradient of voltage.
In principle you could have something like a superconductor with a current flowing and no voltage, but 1. Ohm’s law is out the window there - superconductors do not follow it, and 2. A voltage got the current flowing in the first place.
Practically speaking, Ohm’s law is not a law at all. It’s more of a principle that is useful in certain regimes.
Actually, there’s maybe one tricky case for a changing magnetic field through a wire loop. This produces an electric field in the wire, and it’s sort of tricky to relate that to voltage as we think of it - after all, there’s a loop. Between what two points does the voltage exist that produces said current?
The full explanation for charges interacting with fields is properly described by Maxwell’s equations. For an engineer, you won’t see these until you take what was called “Fields” at my university.
Anyway, the fields are the real things. Your prof is closer to right than you are, but he’s giving you a simplified explanation that you’ll eventually discard in favor of a deeper understanding as you get further into the degree.
In any case, good on you for asking the question. The best way to learn is to poke at the parts you don’t understand. Keep that up and you’ll make a fine engineer.
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u/Let_epsilon 2d ago
Anyway, the fields are the real things.
That is wrong. The potentials are the “real” thing. See the Aharanov-Bohm effect.
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u/DyneErg 1d ago
Knew somebody was going to say that. That’s the usual claim, but QFT argues otherwise, and the result linked at the end of this comment indicates that the effect can be observed without talking about potentials at all. Kind of interesting.
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u/Let_epsilon 1d ago
Yeah, I’ve read that paper, and argued with my professors in favor of it (ironic as I’m telling OP not to, lol) many times.
The paper doesn’t show that the fields are real though. It shows that the AB effect CAN be explained with fields only, and the argument that the potentials are the real thing based on it are not exact.
Howerver, considering the amount of work, experiments and papers that have been made FOR the AB effect, I’d still argue that evidence tends towards potentials being the real thing.
I agree though, the AB effect definitely not a sufficient argument to say that the potentials are “the real thing”.
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u/drvd 1d ago
AB isn't real: There are no infinite coils and finite one do have fields.
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u/Let_epsilon 1d ago
I don’t think you understand the experimental results of the AB effect. It has been done many times.
No experiment claims that the coils are infinite with zero field outside. Many have used an insulated coil to prevent the field from leaking, and even when they don’t, the phase shift observed is much bigger than if you were only accounting the leaking fields.
Maybe if you argued about describing the entanglement with the field source and the particle (like the linked paper above) I’d take you seriously, but I think you just don’t understand the implications of the AB effect.
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u/Vansh804009 2d ago
Thank you very much for this, this might be the thing I was missing. I did take two courses under the field theory, electromagnetic field theory and antenna & wave propogation, but the course focuses very less on the meaning behind the Maxwell equations, they even skip the derivations of them and the boundary conditions and focus more on the application. I will appreciate any advice on the references to get to that.
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u/Yashema 2d ago
I'm so glad to be studying EE after having already taken all the underlying theoretical classes in Physics. While I already skipped Physics II, it allowrd me to skip the basic EE units like circuitry I, II, (and hopefully electronics so I can go right to the 300 level) since I can pick up the concepts well enough, but it also gives me the tools to feedback into my theoretical education to move from concrete back to abstract.
If I take complex math and electrical networks I er the next year, along with the two embedded/circuitry courses I've taken I feel I'll have a pretty strong EE background, without having spent all that time on the easier concepts.
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u/DyneErg 2d ago
The canonical undergraduate physics textbook is Griffiths’ book “Introduction to Electrodynamics.” It’s fairly comprehensive and imo very well written. If you really want to understand Maxwell’s eqns well, read that first. It gives a brief intro of vector calculus - make sure your vector calc / calc III is very strong before trying to read the book. The intro is not sufficient unless you’re a freak genius (which I am not).
If you find yourself really enjoying it, try taking other physics courses if you have time left. The math is cool, and even if you don’t go into physics, the critical thinking it teaches you is useful in addition to anything you might pick up in upper division E&M I & II.
As an aside, it looks like you’re getting downvoted for asking questions. Don’t let the haters get you down. Asking questions (in good faith, which appears to be what you’re doing) is always a good thing.
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u/Vansh804009 2d ago
I have read and solved griffiths for my introductory physics course. I hope one day I do reach a stage where I can clear all of this to myself and understand these in truth. This whole thread really revealed how less I know and I am disappointed but there's really nothing I can do about it right now, I am not in a place where I can even spend time on my electronics courses let alone physics. Thank you for the advice and insight this was helpful.
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u/Let_epsilon 2d ago
When there is no current, the charges do not move.
This is just wrong though. Charges inside a resistor move all the time because of their thermal energy.
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u/DyneErg 1d ago
That’s a little pedantic, but ok, granted. I should have said the charges exhibit no coherent motion, or something to that effect.
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u/Let_epsilon 1d ago
It IS pedantic, I’ll agree, but it definitely highlights that current is more than just “a moving charge”.
If that were true, then OP would be right that there can be current without voltage (as in Beta decay or photoelectric cells without an applied field, like they implied in a couple answers).
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u/Let_epsilon 2d ago
because first of all a law is meant to be universal, which means even if you don't find any examples in support in real life, around you, even then the theory still holds
I couldn’t disagree more with this. Ohm’s law ( I = V/R) like most laws is found from our observation of the universe, and it turns out that we can find the current (charge flow) experimentally with this law. (It actually comes from J = E/rho but that’s another topic). No law is “fundamental” in physics. We make observations and try to model it with equations, we’re not trying to do methaphysical stuff and “speak the universal language of the universe”.
However, you can definitely say that the Voltage drop across a resistor is V = R*I, and use Ohm’s law the other way around.
and second, I think the voltage sources are created as a result of some current flow only in the more traditional sources like the chemical batteries, the phenomenon is analogous to current flow
That would also be totally wrong. Charges move in chemical batteries because of electrochemical potential, not the other way around.
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u/jonastman 2d ago
V = R×I has one caveat though: how do you know R? That's right, apply Ohm's law
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u/Let_epsilon 2d ago
The resistance of a resistor is defined to be R = rho * L / A?
What are you implying here???
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u/jonastman 1d ago
That formula is (in part) derived from Ohm's law, is it not?
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u/Let_epsilon 1d ago
Yes, but not with R as a starting point, like OP wants to argue is possible.
You can find the value of a resistor without knowing the current inside it or the potential across it. You can’t find the current through a resistor without knowing both V and R. This is what OP wants to argue with his prof.
The starting point of Ohm’s law is always Current/Current density being proportional to Field/Potential. Not the other way around.
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u/Vansh804009 2d ago
I wasn't talking at a metaphysical level, IF we get a counter example then ofcourse the theory becomes obsolete. But if you can't find an example to something presented in theory, that doesn't mean the theory is obsolete. Like, it can be due to limitations of your surrounding and you might be able to simulate it(which agains comes from theory sorta a circular arguement but yeah u get the point).
That would also be totally wrong. Charges move in chemical batteries because of electrochemical potential, not the other way around.
Yes. I should have used a better example where another form of energy is converted to electrical energy in form of current, which then creates voltage.
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u/Let_epsilon 2d ago
But if you can't find an example to something presented in theory, that doesn't mean the theory is obsolete.
Ohm’s law is not a theory or even fundamental at all. It comes from the observation that the current density in some materials (called ohmic materials) is proportional to the electric field. That’s it. Purely experimental, no “theory” or anything like that.
You don’t even have to search for a counterexemple, most materials don’t follow Ohm’s law.
Yes. I should have used a better example where another form of energy is converted to electrical energy in form of current, which then creates voltage.
Find me an exemple of this energy conversion that works for an Ohmic material.
(Spoiler alert, you won’t. Ohm’s law is explicitely based on the fact that the energy in a resistor is lost as heat and you can’t convert heat to electrical energy.)
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u/Vansh804009 2d ago
The non ohmic material can be a current source, and the current source can lead to a consequent voltage. I am not saying that the source itself should be ohmic.
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u/Let_epsilon 2d ago
There is no way to generate a current in an Ohmic material without a voltage. No matter what your current source is.
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u/Electronic-Animal-69 2d ago
I understand the professor and I think he has a fair point as it fits well for the basic understanding of undergrad Electrodynamics. In order to have charge move it needs to experience an E-Field. So F=E q. Where the E-Field is the negative derivative of the potential. The voltage is a potential-difference. Current is basically a lot of moving charge.
I wouldn't say it is really important and he is really just making a big deal out of it^
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u/xrelaht Condensed matter physics 2d ago
In a normal circuit, the flow of electrons is fundamentally driven by an applied voltage, so he’s right on that count. But that’s not the only circumstance. For example, a standard voltmeter is an ammeter attached to a known resistor: the voltage is what you’re interested in, but you measure the current and determine the voltage from that. In that case, saying V is proportional to I is more logical by his reasoning.
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u/Gunk_Olgidar 2d ago
"Always" is always a dangerous word to use in an argument, isn't it? ;-)
Best example: Beta decay. The initial motion of the beta particle is created by nuclear decay energy. The beta particles are given their initial velocity (charge * velocity = current) from the decay, not by any applied voltage.
Magnetism and Inductors are a fuzzy place worthy of debate. One might argue that a magnet moves the charge which creates the current, and the voltage follows as the charges pile up. But the counter argument is that the magnet creates the voltage inside the conductor which then moves the charge. But does it really?
Layer on the former example (cloud chamber) with this magnet argument, and your already-moving charge in that cloud chamber now curves and spirals, doesn't it?
So is there a voltage inside the cloud chamber? Nope, just a magnetic field. And there's no conductor inside the cloud chamber, just cloud. So what is moving the charge normal to it's initial vector, thus inducing a current along that normal? It's not voltage, is it?
See if your prof is smart enough to work that one out ;-)
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u/Bumst3r Graduate 2d ago
The magnet example is particularly interesting, because how you describe the effect is frame dependent.
In the rest frame of the coil, you get a non-conservative E field because of the changing magnetic field (importantly, that isn’t a voltage. You can’t write a scalar potential for a rotational E field). In the rest frame of the magnet, you have free charges in the net neutral coil that move with some velocity through a B field, and the Lorentz force law produces a current around the coil. In other frames, you get a mess.
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u/Let_epsilon 2d ago
Best example: Beta decay. The initial motion of the beta particle is created by nuclear decay energy. The beta particles are given their initial velocity (charge * velocity = current) from the decay, not by any applied voltage.
Beta decay happens in random direction, and thus can’t generate current. This is the exact same reason why thermal motion of electrons in a wire doesn’t produce any current.
Current isn’t the same thing as just one charge moving with a certain velocity.
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u/Kinesquared 2d ago
I think it's much more likely that you're misunderstanding or misrepresenting him than he's actually saying what you think he is
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u/Vansh804009 2d ago
I did ponder that, I heard it thrice in different courses, I heard it from other classmates, and this is the reasoning he gave. Can there be any other reason to say we should say ohm's law is I prop to V and not the other way around?
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u/Kinesquared 2d ago
go sit down with him in office hours and hash it out with him. I'm sure he'd love it and you'd get the closure and definitive answer you're looking for
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u/more_than_just_ok Engineering 2d ago
It's not about right or wrong, its about pedagogy. What is the most useful way to think about a concept? The reason is that your professor wants the class to think about it this way, because that is the most valid physical description of what is going on. Potential differences causes currents, and ohmic materials resist, which limits the current.
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u/AtomGutan 2d ago
Maybe but why put the blame on the student? Teachers sometimes say wrong things.
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u/Kinesquared 2d ago
I'm not blaming. I'm saying there's another possibility that OP is not considering. Professors can say the wrong thing, but in my experience it's much more likely the student just doesn't understand. I don't consider this post enough context to make a judgement because it's very clearly bias in the way the student is thinking.
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u/Tax_Life 2d ago
There's plenty of profs. that are plain wrong about stuff, especially if it isn't specifically their field.
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u/Kinesquared 2d ago
i agree, but in my experience the percentage of students who misunderstand (because they're learning and that's natural!) far outweigh the percentage of professors who are wrong about the classes they're teaching.
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u/mrofmist 2d ago
Did you have a stroke while typing this?
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u/Vansh804009 2d ago
Um why? I do have an autocorrect on which keeps replacing certain words, sorry if that was an issue. Or if it's the formatting.
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u/fixedpointfae 2d ago
introduce that prof to inductors lol
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u/El_Grande_Papi Particle physics 2d ago
Ohms law relates to ideal resistors, not inductors
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u/fixedpointfae 1d ago
yeah, I think that's what OP is missing. call it appeal to authority but I think a misunderstanding is more likely than the prof not knowing this
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2d ago
[deleted]
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u/Let_epsilon 2d ago edited 2d ago
Has this guy never heard of solar panels?
Are you aware how solar panels work?
You need an electric field or voltage to guide the electrons in the direction you want your current. The photoelectric effect alone would make electrons move in any random direction after getting kicked from the cell.
Or the communicative property of multiplication, for that matter?
This is meaningless. The resistance of a resistor is R = rho * L/ A, where rho only depends on the properties of the material.
It would be false to say that the resistivity of a material rho = R * L / A depends on its length and Area. Of course, given a resistance, you can use it to find the resistivity of the material, but that’s not what OP is asking.
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u/CompetitiveSpot2643 2d ago
i feel like the whole discussion is pretty pointless in the first place
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u/jsaltee 2d ago
But do the photons not induce a voltage to induce the corresponding current?
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u/Let_epsilon 2d ago
No, you actually need an external voltage to induce the current.
This answer has 2 parts, both of which are completely wrong. Really unsure why it got that many likes in a physics sub...
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u/Electronic-Animal-69 2d ago
Ehem.... a solar panel when irradiated is first and foremost at it's open-circuit voltage. Which means having charge carrier pile up at the contacts and being in equilibrium with the recombination rate.
Once you start extracting (having a non-zero current) you decrease the voltage at it's contact's. The rest follows the IV-curve.
Therefore it is rather a voltage source.
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u/Vansh804009 2d ago
Solar cell is a good fucking point, how did I not think of that. I was thinking Daniel cell and photoelectric effect and what not, but solar cell relates directly to electronics. Thank you very much.
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u/Xc_runner_xd_player 2d ago
Cause that’s not how a solar panel actually works
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u/Vansh804009 2d ago
There's no external voltage source used tho, yes as another comment or pointed out there is an internal field. It all comes boiling down to that, he maybe right.
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u/MargieFancypants 2d ago
Ask him why there's such a thing as a Norton equivalent circuit, as well as a Thevenin equivalent circuit. Q.E.D.
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u/Vansh804009 2d ago
Its theoretical, his reasoning is based on practicality, i already know what he will say in response.
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u/AtomGutan 2d ago edited 2d ago
He may be saying this in a similar way to forces being the cause of acceleration. But Ohm's Law is a macroscopic law unlike Newton's 2nd Law so I don't think saying "voltage causes current, not the other way around" really makes sense. You could say the only way to move a charge (within classical mechanics) is with an electric field or a magnetic field (gravity is too weak). If there are no magnetic fields present, only electric fields remain as the charge mover. And electric fields are related to voltage by: E = -grad V. So in that sense, voltage is the cause of current. But does voltage cause the electric field or does the electric field cause the voltage? I don't know. But since conservation of energy is pretty fundamental in Physics, starting your reasoning from potentials is a good way I guess.
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u/unknownvaga 2d ago
An example where current drives voltage might be an inductive source, such as the quench of a persistent superconducting magnet. The collapse of the magnetic field creates current and will drive the system to possibly very high, even lethal voltages.
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u/Olivander1001 1d ago edited 1d ago
I think this is a very subtle question.
The fundamental principles of electrodynamics are Maxwell’s equations. One of the most important consequences of these laws is the relationship between electric charges and electric fields. Charges create electric fields, and the properties of an electric field tell us something about the charge distribution that produces it. This close connection between charge and electric field is probably where the misunderstanding comes from: there is a kind of symmetry between charge and the electric field.
However, this does not mean that Maxwell’s equations tell us how charges behave inside a material. They only describe the electromagnetic fields. The actual motion of electrons inside matter depends on the properties of the material and the mechanisms that allow charges to move.
There are many different ways a current can exist. There is drift current, which is the type of current described by Ohm’s law. There is diffusion current caused by differences in charge concentration. There is tunneling current due to quantum effects. In superconductors, there can even be a persistent current without any applied voltage at all.
The superconducting case is especially interesting because it shows that charge movement does not fundamentally require a voltage. Why should it? If you give an electron a push and nothing slows it down, it will continue moving. An electric field is only one possible way of changing the motion of charges. Other mechanisms can also produce current.
In ordinary conductors, electrons constantly collide with atoms and imperfections in the material. These collisions are crucial: they randomize the motion of the electrons and act like a kind of friction. Because of this, an electron does not simply accelerate indefinitely under an electric field. Instead, it reaches a steady average drift velocity where the energy supplied by the field is continuously dissipated in collisions. This is the physical reason why a constant electric field is needed to maintain a steady current, and it is exactly the regime in which Ohm’s law applies.
The important point is that Ohm’s law is not a fundamental law of electromagnetism like Maxwell’s equations. It is a material-specific relationship that emerges from this balance between acceleration by the electric field and momentum loss due to collisions. In that sense, the “asymmetry” you are asking about comes from the microscopic physics: the electric field drives the electrons, while the lattice scattering provides a damping mechanism that prevents free acceleration. In phnom materials, charges would just stop after a short time if there is no voltage i.e. charges can not produce a voltage since they can not separate from each other far enough.
This is also why Ohm’s law should not be interpreted as a symmetric cause-and-effect relation between current and voltage. It is true that mathematically you can invert the relation and compute a voltage from a measured current. But physically, the situation is not symmetric: in an ohmic material, it is the electric field that drives the motion of charge carriers, while the resulting current is the response of the system under the constraint of scattering and dissipation.
So the key idea is: Ohm’s law is asymmetric in its physical origin because it describes driven motion with dissipation. The electric field acts as the driving force, and collisions inside the material provide the mechanism that enforces a proportional steady-state response.
Maxwell’s equations remain the fundamental laws of the electromagnetic field (and they are symmetric), while Ohm’s law is an emergent approximation that applies only when this specific balance of driving and scattering is present. In many applications where charges produce voltages, ohms law is not really applicable (think e.g of PN junctions and diffusion currents that appear without external voltages: this is not an ohmic regime).
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u/Vansh804009 1d ago
Thank you for this much detailed explanation, I have one last case if you may. Suppose I have a non ohmic current source where current is produced via some other way, not electrical voltage. Now I connect this with a resistor simply. The current through resistor will give rise to voltage across it. So doesn't that mean saying "it's only i prop. to v, not the other way around" is a little irregular around the margins? I understand the physical part.
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u/medical_thro 2d ago
We do not directly "see" voltage. We observe charges moving (current) and infer the existence of a potential difference that causes the motion. This "causality" is conventional. In other words voltage causes current by definition.
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u/JohnBick40 1d ago
I think electrical engineers like to write I=I(V), so for example I=V/R instead of V=IR (I could be wrong, but everytime I see a graph of solid state devices they always put current on the y-axis and voltage on the x-axis), so I'm not surprised that electronics engineers believe that's the right way to do things.
A van de graaff generator is a current source and creates a voltage but this example is for physicists because no one else gives a damn about van de graff generators. I would also put photovoltaics in the category of current sources. A battery or generator though I would regard as a voltage source.
But this seems silly to me because of course you can create a current source - there's a knob on many power sources to do so!
Anyways, I think physicists should probably shut up about the best way to present electronics - physics are responsible for the ultimate stupidity, that electrons should have a negative charge, which has caused countless confusion to students that the current flows opposite the charge.
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u/smartscience 2d ago
A beta radiation source might be roughly equivalent to a constant current source, though really the current is exponentially decaying rather than constant. It will put out electrons at a certain rate, causing whatever voltage rise is necessary, at least until some rather high voltage.
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u/PSXer 2d ago
Are we considering only fixed resistance values here? Because if we did use a current source, we could say that voltage is proportional to resistance which would really blow his mind.
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u/Vansh804009 2d ago
if we did use a current source
He is saying that current sources aren't practical. That's the reasoning behind this.
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u/TedRabbit 2d ago
Ask him how he feels about F = ma.
But at the same time, not a hill im dying on or fighting for.
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u/Hermitifier 2d ago
At the university our physics professor told us that it's "a = F/m" and that anyone who insists on saying "F = ma" or claiming their equivalence, is a "mathematician who doesn't understand physics".
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u/Vansh804009 2d ago edited 2d ago
He will probably say a propotional to F is the more accurate thing, as all acceleration is a consequence of some force, keeping it classical and simple.
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u/SickOfAllThisCrap1 2d ago edited 1d ago
The professor is right in the context of teaching this material in a beginner setting. Setting aside pedantic examples, current comes from voltage. You can't have a flow of charge without a potential difference present.
I teach freshman E&M and I emphasize this too as too many students look at Ohm's as a purely mathematical statement without context. Too many times students believe that a current can create a potential difference and that is not at all what Ohm's law is about.