Resistors – Ohm’s Law is not a real law

Resistors – Ohm’s Law is not a real law


Ohm’s Law is one of the most basic principles in electronics, yet it is not an actual physical law. Understanding ohm’s law is critical to understanding how electric circuits work. Understanding why it is not an actual physical law is critical to understanding the basic principles of logic and the nature of physical laws. Suppose we have a battery and a device which we call a resistor. The battery will create a voltage, causing charged particles to flow around the loop. On the other hand, the resistor tries to prevent the charged particles from flowing. The number of charged particles that pass by each second is what we refer to as the current. There are three ways to increase the current. The first way to increase the current is to use more batteries to create a larger voltage. The second way to increase the current is to use a resistor with a smaller resistance. The third way to increase the current is to use several resistors in parallel. Having several resistors in parallel is the same as having one resistor with a much smaller resistance. On the other hand, having several resistors in series is the same thing as having one resistor with a much larger resistance. Let us create a precise mathematical definition for the word “resistance.” Suppose we take the voltage across the resistor, and divide it by the current passing through it. The result of this division is what we will define as the resistance. This is what we refer to as Ohm’s Law. However, this is not really a physical law, but simply the arbitrary definition that we created for the word “resistance”. Physical laws tell us how the Universe works. Ohm’s Law would tell us how the Universe works if, for example, the value for the resistance of a material always stayed constant. However, this is not the case. As current passes through a material, the material heats up. As a material’s temperature changes, its resistance also changes. With most resistors, this effect is relatively small. In the case of some resistors, this effect can be very large. If this effect is large, we can use it to our advantage by using the resistor as a temperature sensor. By placing a voltage with a known value across the resistor, and measuring the current that passes through it, we can calculate the resistance of the resistor. This would give us information about the resistor’s temperature, and therefore also give us information about the temperature of the material that the resistor is in contact with. Temperature is just one of the many factors that can cause the resistance of a material to change. However, when we say that the resistance “changes”, all this means is that if we take the voltage across a resistor, and divide it by the current passing through the resistor, we will not necessarily always get the same number. The fact that the number that we get at any given time is always equal to the resistance of the material is simply due to the fact that this is how we defined the word “resistance” in the first place. There are many examples in logic where a statement is always true simply because of the way in which we created our definitions for the words, and the statement doesn’t actually tell us anything about the external world around us. This is one of the logical fallacies we need watch out for, both with regards to science, and also with regards to life in general.

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100 thoughts on “Resistors – Ohm’s Law is not a real law

  1. That last statement is a key tenet of logical positivism. Wannabe philosophers around the world will crap themselves if they hear you say that stuff. That's just one reason why philosophy gets a bad reputation among scientists.

  2. Very nice video ! But the music is a bit distracting, the 5th symphony is a bad choice. Some other calm classical music would be a good alternative.

  3. A more accurate way to explain that Ohm's law is not Universal is with negative resistance. This can occur in plasmas and electronic components where the current-voltage relation is highly nonlinear. See https://en.m.wikipedia.org/wiki/Negative_resistance

  4. This is a very impressive animation that actually clear the doubts and expose the actual practical concept behind. Thank you for making such videos.

  5. Your channel is great source to understand difficult concepts by esay way. Please make electrical machine related videos.

  6. Please Eugene remove the music from these videos!! What is it with Americans and the urge to have background music on instructional videos!! Please. It's extremely distracting when trying to learn the knowledge you are trying to convey.

  7. Thank You for this video. People seem to think by solving the circuit is the same as understanding it, which is a fallacy that needs to be corrected. I've always was more interested in understanding a circuit & it's fundamentals which can be very hard to grasp because of how they describe it, for example, Ohm's law something you alluded to briefly in your video, you mention how it is not a actual law. Thank you for pointing that out.

  8. I, too, don't want to seem contrite, but I have to correct the claim of a logical fallacy on tried-and-true physics.

    Ohm's law actually is a vector electro-magnetics equation. Since I can't write Vector notation here, assume that capital letters are vectors in the following, and I'll write out the Greek letters, and T is temperature.

    J=sigma(T)*E where J is the current density, Sigma is the conductivity that is a function of temperature, and E is the electric field.

    First thing to point out is that the conductivity of a material is temperature dependent, and that temperature dependence is taken into account in Ohm's law.

    Second thing to point out is that the version of Ohm's law used in circuit analysis is a simplified scalar form, with a few important assumptions and simplifications.

    That does not mean that the scalar form used in circuit analysis is incorrect.

    Furthermore, just because one observes and minor inconsistency in a heavily simplified application of a physics edict does not mean that physics edict is incorrect.

  9. Wonderful animation correctly describing how Ohm's law (a law just as real as any other law from Physics) works. It's not any less valid because R=V/I. This isn't the definition of resistance, btw. Resistance = (resistivity * length)/cross-sectional-area.

  10. My high school teacher told us to think of resistance intuitively as of the amount of collisions that the electrons experience as they go through the wire, for example.: resistance increases with temperature because the atoms in the wire (or within the resistors) are vibrating more and thus are more likely to impede the path of the electrons; also the longer the resistor or the smaller its cross-sectional area, the more collisions. Is there any way to relate this approach to the existing definition of resistance as voltage/current ?

  11. Showing the red balls, you want to prove to us that there is no Ohm's law? Nobody knows how atoms and electrons work, and how they move. But Ohm's law really works in practice.

  12. This is a lovely demonstration, but isn't ohms law " The PD of a metallic conductor is directly proportional to the current flowing through it, AT A CONSTANT TEMPERATURE"? So ohms law actually addresses the change in temp, which is why a filament bulb is a non ohmic device.

  13. Ok so in any case anyone is still in the comments. Could someone clarify this for me?

    What this video is impling is that: "Ohm law does not define resistance outside of it, therefore it's not a law". In the principal example of Newton's second Law, that even without (F=M*a)acceleration could still be defined in some way. The reason of not being a law is that the Resistance does not have a constant for the actual resistance, since it would decreasse with temperature.

    So if in some way we define a constant for the material with the resistance at certain temperature; and another one for the amount that it changes with temperature and relate that through the current passing. Then it would be defined as a law? Like: R = Constant – ValueOfChange*DiferenceInTemperature. This way we could explain how the material change, and find a way to discover temperature by the new resistance.

    I mean this is what we did with most atomic numbers. Found the value for a constant and related that with somethin. Molar mass and avogrados.

  14. Your way of thinking was discussed about 1830 to 1850 when people did not believe how simple electricity is actually. That's the time where you live in – mentally.
    So actually the current through a resistor measures the temperature of the resistor.
    Nice try.
    Now have a look at pendulum clocks. They have been used for centuries as most precise time meters. But actually a pendulum clock also measures temperature. The pendulum will lenghten if temperature rises. Then the clock will run slower, If the pendulum is not temperature compensated.
    Do you recognize the similarity to your argument?
    The truth is, pendulum clocks do not measure time at all. Pendulum clocks (temperature compensated) measure the local gravitational potential. This happens, because gravitation pulls the pendulum back from its upswing.They run slower on top of the mountain and run faster down in the valley.
    Time runs just opposite: time runs faster on top of the mountain but slower down near Earth center. This proves pendulum clocks do not measure time, be they temperature compensated or not. But the both effects differ for many decimals and therfore go unnoticed for people living at 1850 – mentally.

  15. Doesn’t heat reduce resistance… This in turn leaves many variables for which one law would be somewhat inadequate.

  16. Hello Eugene! Wonderful video, but I still have a basic question. This question is based on the following assumption: A difference in electrical potential energy produces a current.
    Like water flowing down a mountain. QUESTION: If the above statement is true, why does current NOT increase over a single resistor in series with a battery. After all the resistor creates a difference in electrical potential energy!!!!

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  18. I find the statement "Ohm's law is not a real law", to be, well, somewhat misleading.

    I mean, yes, the statement R=V/I more or less defines 'resistance' but that such a value would be considered 'constant' in an varying of either current or voltage is a rather meaningful statement.
    So, for a current through a conductor, and the potential drop across that current, we find what appears to be a non trivial relationship: there is a constant proportion between them, determined experimentally.

    Of course, Ohm's law isn't true in general, but that it doesn't apply in some more nuanced cases doesn't distract from its status as a "law". The fact that it doesn't describe a very 'fundamental' behavior' does not distract that it takes something seen empirically describing relations between quantities in the world. There are many laws that describe nonfundamental relations in the world, in particular many of the gas laws, that are nevertheless important as 'practical laws'. That V and I share a constant proportion, which is determined experimentally, is an example in electrostatics of such a 'practical law' or 'experimental law'.

    That this was even the case, that V and I shared a constant proportion, was met by lots of critique and hostility. Something that would be absurd from a mere 'definition'.

  19. At 3:15 I suggest the pink arrow of the voltage of the resistor to be pointing down only to indicate that it's voltage drop

  20. What's presented here is a simplified model of the V I circuit relationship. You can write a more accurate model that takes account of the many other factors, but this version is good approximation for most DC circuits. Temperature co-efficients are easily accounted for but AC circuits, and RF circuits in particular, are where things get trickier.

  21. But in the Ohm's Law it is mentioned that the temperature should be constant.
    So how the Ohm's Law is wrong?
    -please explain…

  22. this feynman lecture is apt for this video:
    http://www.feynmanlectures.caltech.edu/I_12.html

    it tries to solve this paradox a bit.

  23. Yes, thank you. Some straight answers for once. I don't know why there is all of this misinformation when learning things like this. I'll have to check out your other videos. Thanks again.

  24. anyone watching this as a review just set the speed at 1.75 and everything is better. the music and you can understand her better

  25. How can you tell simple what a resistor is, Can you say like ”A resistor is something that controls the current”? I have a test tomorrow and still don’t undersatsen what a resistor is

  26. What's your point exactly? As the resistance changes (due to temperature in this case), the current (or voltage) will adjust accordingly. Ohms law is not broken.

  27. Thank you for showing me way to magical science out of craming these not real laws which fails to understand this magical world of science and innovative thinking.

  28. Ohms law can be stated for puplis more correctly for many devices as " the resistance of a metal device of constant temperature remains constant". And resistor can be defined " a device for which Ohms law is valid". In the transation to greek language I made sime small changes in terminology to make video "compatible" with greek educational school system and definitions.

  29. Ohm's law, as you stated it, is not a real law, but I don't think what the law is supposed to be. My physics book stated Ohm's law as saying that for many materials the electric field is proportional to the current density (or, equivalently, voltage is proportional to current). I guess you could still argue that this isn't a real law because it isn't always true, but it is still an empirical observation rather than a definition.

    What always annoyed me was Kirchoff's loop rule. If you have any numerical property, with a number assigned to each point, like electric potential, then the laws arithmetic demand that the sum of the differences in that property around any closed loop is always zero. Yet, it is always treated like a law of physics, even though it is just a law of arithmetic. I like calling it "Kirchoff's loop tautology".

  30. I was thinking, if we expose to pure vacum a pair of electrodes with some voltage kept constant between them, the vacum will be filled with electrons and therefore will not be not pure vacum anymore. However, the density and velocity of these electrons on the plasma-like medium will be proportional the applied voltage and therefore you can measure this proportionality. This proportionality is an enlightening description of the behavior of the universe around us. How can a successful description of a very intrinsic visceral operational aspect of the universe not reveal any specific physical law? Is this proportionally a mere rearrangement of terms of some other true laws of physic? Can a physicist or a mathematician calculate that?

  31. I need basic concepts of resistance…… Just like any conductor like cupper their own electron which is not explained here….

  32. If resistance doesn't physically exist, what does exist? The inverse of resistance? The load on a circuit? The radiated energy of a given voltage?

  33. Not convincing. R=V/I is not the definition of resistance. It is a physical law that relates those three properties of a system. Arguing that it isn't a fact of the universe because the resistance of a material doesn't stay constant is just ignorance of the more complex relationships involved.

    The actual definition of resistance is R=resistivity •length/area. All three of those variables can be affected by temperature, and resistivity also depends on material composition.

    I suppose you could try the same game by substituting the definition of resistance into Ohm's law:
    r•L/A = V/I (here I am using r for resistivity) and then define resistivity as r = V•A/(L•I). But that doesn't stop resistivity from being a real property of a substance. The "definition" gives a way to measure resistivity.

    In principle, at least, resistivity could be predicted from more fundamental physical theory.

  34. I disagree, because the law is based on the values assumed at the time of measurement, so if the resistance changes, the result changes, but even the voltage can change in the real case, what defines the law of ohms is that the current in any case is defined by their relation in the ideal case, therefore comparable to an infinitesimal or derivative time of t, so if we consider the real case, we must consider the transient and the residual inductance, therefore an energy component that supports the field magnetic. perhaps it is better to say = dv / dr, after the transient … the law is valid …

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  36. I FINALLY GET IT WHY YOU NEED TO SUM ALL THE VOLATGE CREATED BY THE RESISTORS WHILE STACKED IN SERIES .

    THANK YOU SO MUCHH

  37. Every engineer student should watch these videos or every instructor should show these videos to their students. Understanding these concepts by reading only is very difficult. Seeing it working like this is so much easier to understand.

  38. Pure resistance value ' mean off any materials used for construction of any electronics components is not pure in nature. If physics equal to nature so we are a being far from nature. Construction of many components equal to many error that's beyond of our knowledge.

  39. If ohms law is a definition.. Then newtons second law must also be a definition for term called force.. It will not define nature of universe but defines what is force.. So newtons 2nd law is also a definition.. Is it…

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