1. I totally agree with your point of view regarding KVL. I wonder that if you connect the probe perpendicular to the circuit, the induced voltage in the probe will be negligible. Hence, you can read V_R+V_loop. It will be helpful if you show a similar video considering perpendicular probing.

  2. Kirchhoff is a dick head splitting hairs over sense wire positions. Kirchhoff needs a full bridge rectal fryer. ALL HAIL THE UNIBROW!

  3. Your "noise" measurements are the inductance of the two wires in parallel and EMF induced into the circuit and the untwisted portions of your lead. Reason why it differs is they are in different positions one time closer, another time farther away, or other times not totally parallel with each other. In order for you to get an accurate reading you should use shielded leads from point to point or have your untwisted leads, 90 degrees from the measurement point. And if you really want to get picky, the probe itself will affect your measurement as it becomes part of the circuit. Because, depending on the frequency and voltages being measured, you can introduce capacitance or attenuation.
    I see what the professor is saying… when a circuit is being effected by EMF due to the circuit component characters, wire and connection resistance, until the EMF finally peaks, the circuit will behave and measure differently in different spots and will not equal zero. Depending on the placement of the EMF and the measuring devices you can get, either a positive or negative peak. You can see it in your noise measurement, those ripples are the varying voltages until the circuit stabilizes. Due to each component characteristics and connecting wire length the circuit at times, the total voltages will not equal zero.
    In addition, EMF waves are formed in the circuit which can be out of phase until the circuit "catches" up. And you also have angular velocity, field flux, stray field and cross lines to account for until the field stabilizes. Plus, just arbitrarily setting the circuit over the coil doesn't allow for accurate readings…
    When the law was written, they did not understand I-V characteristics, nor could they measure it or the circuit accurately.
    Plus you are measuring with a single scope… measure it will multiple scopes and compare the timeline of the voltages measured in the circuit and you will see.

  4. If EE's thought about induced voltages like Lewin…
    If you measure something odd in a circuit, don't just think, that you've made some sort of new discovery, but instead first sanity check your test setup. The problem usually lies there.

  5. If I watch this video without then moving on to watch ElectoBOOM's follow-up video, I remain uninformed about certain key points. If (for instance), I fail to read Dr Belcher's contribution to the story (as advised by ElectroBOOM) then I'll not have had the opportunity to get a better handle on the physics. If I'm stuck here I am missing some important bits of the puzzle – such as how electrostatic fields play a role in setting up uniform current around the Lewin circuit loop. What benefits do I gain by failing to go on to discover more? I would be intellectually lazy and self-satisfied in my self-imposed ignorance.

  6. I'm agree with you. Mr Lewin knows tons of phisics, but i guess that he doesn't truly understand about measuring and transformer model and behaviour.
    Anyway the man is a genious and i love him becouse he inspire me to be a better teacher, but hey, even Mr Lewin isn't perfect.

  7. Kirchhoff's voltage law may be true but there is another called Kirchoff's law of thermal radiation/emission and it is indeed false which has huge implications in astronomy, namely that stars are not flaming balls of gas (or gaseous plasma) but rather solids namely liquid METALLIC hydrogen – please watch the Sky Scholar youtube channel for more info and PROOFS.

    There are several videos dealing with Kirchhoff's law, such as this one:

    These principles are proven in the field of MRI (magnetic resonance imaging) technology, but until recently have never been linked to or compared to their (faulty) application in astronomy. This will change everything in astronomy, since we have been measuring or interpreting the radiation of the sun all wrong.

    gas laws and thermodynamic laws are also violated by the very idea of a gaseous star:

  8. What is the essence of Kirchhoff’s Voltage Law
    I rather like the description by British physicist John Roche in his 1987 paper to the Physics Education Journal (22) entitled, “Explaining electromagnetic induction: a critical re-examination”

    I quote from the section entitled: The term ‘electromotive force’ – as follows,
    “It was shown by G Kirchhoff (1824-87) in 1849 that localised EMF’s generally set up auxiliary electrostatic forces, by means of surface charges, in order to establish a uniform current around the circuit (Kirchhoff 1879 pp 49-55, 151-4). Since these additional fields are conservative, the sum of the net potential differences around the whole circuit will be exactly equal to the sum of the PDs across the localised underlying EMFs only. This is the substance of Kirchhoff’s second network law (Kirchhoff 1879 pp 15-16).

    In particular, if there is an accumulator, a generator, or a coil in a circuit, the surface charges in these devices will set up electrostatic fields which so mask the driving EMFs within them that the resultant internal potential difference across each (that is the work done on unit charge passing through it) will be exactly equal to the PD across its internal resistance only.”

  9. What I got (reinforced) from this is that even the wire is a circuit component. Since the sense wire folds back on itself and follows about the same path back around, it induces nearly equal but opposite current from the wire that it's adjacent to, cancelling itself out. So you only read the effects of current through the opposite resistor. At least, that's what appears to be happening. He touched on that near the end when he drew in the hidden transformer.

  10. The issue in short is that due to changing magnetic field virtual inductors not physical are created in the loop due to Lenz Law.This is what is called self inductance.Piece of cake.

  11. Hi there, I am an elektronic technician (one step below an engineer 😉 and I know the video from Lewin. Lewin is wrong! He has forgotton that in a loop with an changing magetic fiel the loop themself exactly each part of the loop is a part of the voltage source of the loop. You could cut the complete loop into infinite small parts of the whole source containing d Volts. If you summarize all the small parts of the loop which are induce voltage and summarise them, then you get sum of the voltage on the resistors and kirchhoffs law is working. The fail of Lewin is that he does not recognise, that each infinite small part of the loop is a part of the (magnetic induced) souce d U with its own " d internal resistance".

  12. You are just like Thunderfoot. You pick the most obviously wrong stuff that doesn't require any real thought to disprove and then take the dumbest approach toward proving it wrong. Oh, wait, you aren't like that at all… lol. I couldn't keep up with you on half of this. With Thunderfoot I need only look at the tag line and go, well, duh, who doesn't already know this?

  13. YES! I saw the transformer, too. The sense lines are part of the circuit! (I was just an ME, not an EE, although I am a licensed ham for what that's worth.)

  14. I demonstrated at the end of my lecture #16 of my 8.02 E&M course at MIT that two identical voltmeters attached to the same 2 points in a circuit can show very different values. The reason is that in the case of an induced EMF (Faraday's Law) potential differences are no longer determined; they depend on the path. This also applies to the secondary windings of transformers as the EMF in the closed loop of secondary windings is induced.
    Of course, in cases where Kirchhoff's loop rule (KVL) applies, 2 voltmeters attached to the same 2 points in a circuit will always show the same value.
    My demo was first suggested and published by Romer in December 1982 in the American Journal of Physics. This demo has now become a classic; it's done all over the world at many colleges and universities.
    Kirchhoff's original text can be found in the following link, pages 497-514: Clearly he was fully aware of the prerequisite for his "loop rule". KVL is a special case of Faraday's Law. That's why Faraday's Law is one of Maxwell's equations and KVL is not.
    By teaching students that KVL always works without telling them when it does not work, makes many believe that the closed loop integral of E dot dL is always zero. ElectroBOOM and Dirk Van Meirvenne therefore believe that 2 voltmeters attached to the same 2 points in a circuit must always show the same value which is not true as demonstrated in my lectures. They each posted a video on their channel in which they claim to have proof for their wrong ideas which violate Maxwell's equations. Apparently they do not know, or do not understand, that in the case of an induced EMF potential differences are no longer determined; they depend on the path. MIT students who took my 8.02 course (Electricity and Magnetism) would not make this mistake! I therefore believe that to introduce a "modern version" of KVL and then teach students that KVL always holds is not advisable as you may set them up for making the same embarrassing mistake that both Dirk Van Meirvenne and ElectroBOOM made.

  15. I am not sure but i think in this fast pulse from the switch it may create in small time a mutual inductance between the primary(source coil ) and the secondary ! Mutual inductance can be applied as source in theoretical circuits. I mean that if you use a Mutual inductance as source, the total voltage in the wire loop could be zero, but i am not sure of this statement , specially because mutual inductance is applied
    for a continuous variations of magnetic flux like in a pure sinusoidal AC circuit. But it might be just a nonsense argument from Electrical engineer student.

  16. How about four-terminal sensing?

    Would that help?
    Dr. Lewin's accent sounds very Dutch-like btw.

  17. ElectroBoom, when you measure the voltage across R1&R2 from one side you got 25mV but when you used the probe twisted wire to get the voltage between the same point from the other side you got 0V(approx.) but did you notice that in the 2nd part the probe wire run side by side the the coil loop, it means that the probe wire should also get affected by the changing magnetic field and maybe it causes 0V??????

    In motor/generator we take armature backEMF in the KVL equation so, here we should also take backEMF induced in the coil. AND then KVL will be valid.

    please let me know what you think about it!!!!!!

  18. I design metal detectors, and this stuff is fundamental to understanding eddy current behavior in metal targets. Dr. Lewin is wrong, that's all there is to it. First, keep in mind that a changing field induces an EMF, not a current. The current is a result of the EMF. Second, as Klaus Peter points out below, the EMF (and resistance (and inductance)) of a loop of wire is infinitely distributed around the loop, all the way down to the electron level. You gotta account for this. Third, as Mehdi shows, an EMF is also induced in the probe wires, even if it is a 10Meg probe. Bottom line is, KVL works just fine for this.

  19. This is fine. Now, do magnetic field within solenoid calculation. A correct one, contrary to myriad of shady-ones all around us.

  20. You nailed it. The probe lines are not immune from the magnetic field hence they sense what they feel not what they are connected to. Kirschoffs law holds. QED!

  21. There's not an actual static voltage drop across the inductor. It's an induced electric field in the conductor due to Faraday's Law. You can mathematically treat it as a voltage drop and ignore the fact that the inductor is just a turning wire loop – but it's not physically correct.

  22. Now i believe, you are genious,

    The part where, you messured in the two resistor circuit, was actualy a coil, resistor just act's like the load, wow cool mehdi 'sir'

  23. Engineer from Denmark here,- made the same test in my small lab and the same conclusion as you. (After seeing lec. 16)(I have designed transformers and understood the probing problem right away) WL ignored my comment. Nice to see it finally settled. I still enjoy WL classes though 🙂

  24. Kirchoff's law can be rephrased as "if you sum your voltage drops from a point A to a point B no matter which path you follow you'll end up with the same final result". This allow defining the electric potential as just a function of position, by choosing an arbitrary point where its value is zero. The conclusion you arrive at, that is "there is a proper way to do voltage measurement between two points" is actually negating the Kirchoff's law, which assumes that you would reach the same result no matter which way you measure it. Also, your proposed "proper" way of measuring does suffer with the same problems of non-addictivity, the case of two points on a circle is a particularly lucky one: try to split a ring into three equal segments, and measure the voltage across two of them, by connecting the probe cables in the midpoint, as you theorized. You'll find non-zero voltage on any of them, and the sum of the three voltages will add up to a non-zero value (because of symmetry).

  25. I watch this channel in front of my family and they don't think I'm smart because they don't understand English. And you know they are right, I'm not smart 🙂

  26. I feel like this is just kind of an argument in semantics. Both ElectroBoom and Lewin are describing the same concept in different ways. It is simply a matter of whether you are choosing to include an induced EMF as a voltage in the KVL loop or not. If it's included, then it KVL holds. If it isn't then it doesn't hold. Lewin isn't including it, and ElectroBoom is. It's not a case of being right or wrong, just 2 different ways of approaching the same problem.

  27. Why so serious ( no shocks)? You are correct, so nice to put a secundairy in the loop. A very good lesson on how to measure correctly. Thank you very much. The truth depends on your point of view (OB1)

  28. Electroboom is right.

    He accounts for the voltage by drawing a more comprehensive circuit diagram. KVL holds.
    The profressor refuses to see that the circuit diagram must be drawn with a transformer. The modification of the circuit diagram is an insight. It is clever and is more useful than the argument that KVL does not hold.

  29. Not convinced about the two voltmeters indicating different readings? Walter Lewin isn't the only one to have ever demonstrated this at MIT.
    Watch "Chapter 10.0.1: Non Uniqueness of Voltage in a Magnetoquasistatic System" on YouTube
    The video looks as if it predates the material posted which presents Dr Lewin's Physics 8.02 Lecture 16 demo.
    Viewers can also download course instruction materials on a chapter by chapter basis – check out the notes section below the video area if you wish to follow up that option.

  30. 3:04 I think it should be Fleming's right hand rule not lenz's law.


  31. Since I'm watching your videos I am already ready to build an pulse synthesicer that interactes with Sine Saw and Square waves OwO
    Tell me a school that teacges it so easy and fast as you do <3 thanks for the great content I love your videos so much

  32. Being smart, well published and well known doesn't mean you don't make mistakes. We are all as equally mortal as everyone else. P(Lewin is correct all the time) is not 100%, and it seems that in this case the evidence is shown. I recall from publications around the "Monty Hall Problem" back in the 1970's or 80's I think, that there were university professors who vehemently argued on the wrong side of the case; because they made a logical mistake. It happens to everyone.

  33. There are many ways to reduce the errors which may be caused by physical phenomenon. Its a curious thing here … All I can think off the top of my head is that, when wires bisect perpendicularly the induced EMF is dramatically reduced. Also, The whole > giant loop idea, for a circuit is silly < It would be much better to keep the induced portion "induced" and the other parts away so they are not affected. Why not just put the parts INSIDE the coil, like a transformer would be, and make the measurement parts far away from the EMF so the probes(&wires) don't pick anything up as well. U seriously can put the resistors in that coil as well. Its silly to think they have to be outside. wrap em up !! i promise they will stay.

  34. kirchoff law shouldn,t work for induced emf !! because kirchoff law was for curl free E field which implies that the close loop intregral of E filed is zero which is only possible when curl of E = 0 but for induced emf its not zero ….

  35. The problem with using two different sensors is that no two machines, no matter how precise will never behave the same on small scale mesurents, unless they are purposefuly and meticulalisly made the same.

  36. Just a layman, but doesn't the whole dispute boil down to 8:30 and whether or not you consider accounting for the fact that the voltage across the loop is non-zero is something within kirchoff's law or not? Lewin says what that non-zero value is dependent on physical geometry and thus not path independent, not part of Kirchoff's law. Mehi says, if you just model it properly as an inductor in the circuit Kirchhoff's law still holds.

  37. Kirchoff's law doesn't hold cause there is no such thing as scalar potential in a non conservative fiels. The explanation based on potential at a point will always be wrong even though it may give correct results . If you see the derivation of Kirchoff's rule it is required that the time derivative of B is zero. I think Walter lewin has given this answer a hundred times to students that's why he isn't replying. You will get the exact same results but different reasons if you try to explain it with Faraday's law .

  38. Of course he did not respond you, he is dutch and like all dutch people they never admit that they are wrong and say sorry …. trust me, personal experience!

  39. For me, as ex audio engineer, it was obvious from the start. Those wires! Once we fought signal of radio station in phones – it was caused by wrong position of grounding wire in the earth (powerful typography had their grounding wire nearby). I can imagine professor's conclusions. And level of those signal was hardly detectable by any oscilloscope we had. Even shape of the wire matters.

    It was bad measurement by scientist.

  40. "Then He would say, 'you stupid kid!'. He wouldn't say that of course, because he's a nice guy."

    Yes, I too expected him to be nice. But sorry to say, I lost all respect for Dr. Lewin. This could have been a place for scientific debate and mutual respect.

    But what did he do? Criticize the creator because some youtube comments were disrespectful. But why would you disrespect a man who has no control over such things? He didn't even try to answer Mehdi's question despite being humble. Rather he directly disrespected another person with scientific mentality.

    Even after Mehdi wrote a paper with Lewin's colleague, Lewin did not say anything at all. This bullshitness of Lewin still boils my blood. Like, what the actual fuck? You already disrespected yourself once with your sexual harassment case, and now you're still not satisfied? I really, really lost all respect for Lewin. If someone is asking a question sincerely and you disrespect him for nothing, your years of education doesn't mean anything to me, you are definitely not a good mentor. Man, this incident still boils my blood…

  41. So you expect the electrons to travel at the same speed through two different resistors? ( not really, right?)

    Did you try this test with a wheatstone bridge?
    I mean, it can't be that a big difference to split the two resistors into two further ones for each, right?

    I just assume (for now) the shown effects will be different at different temperatures. ^^
    Let's say you heat the 900 R and cool the 100R et vice versa. Nawh, you already made that Peltier Plate. Dang.

    I learned, wherever an electric current flows, there an electromagnetic field is.
    I also learned if electrons have to flow through different "tube diameter" ( a.k.a resistance) the speed of the current flow is different and the transformation of the
    POWER ( they call that dissipation, lol) also is different at the certain points of the tube.

    Let's forget about gravity and the earth magnetic field. For now.

    BTW.: do you know Sam Barrows I am sure you will like their experiments.

    And last but not least, a heartfelt thank you for your awesome YT videos.

  42. tnx EBoom: A suggestion: write the number l like you see at the left, which doe not look like a 7. So then for 7 you add a cross on the 7. When you make a l, put no flag on its top, just l please. Make a good old practical American l . l, 2, 3, 4. Throw 1 into the trash can.

  43. To me
    Kirchhoff's Law means that the current in any part of a circuit is the same, which I think holds only for passive components

  44. To me
    Kirchhoff's Law means that the current in any part of a circuit is the same, which I think holds only for passive components

  45. Kirchhoff’s law is flawed.
    Mainstream teaching of EMF is flawed.
    Dielectric and Magnetic is incorrectly taught.
    Dielectric coupling is incorrectly taught.

  46. Mr Lewin means if u bring and move a magnet through the circuit or through the L component then the total voltage all around the circuit is not zero anymore. It's Faraday law. The second point is we cannot determine the voltage difference direction between the "poles" of L from KVL "alone" but from Faraday's law. What engineers do is just memorizing the roles not the principles.
    Krichovs law is applicable when the circuit is isolated energetically.

  47. The professor is right.
    It is mainly because of a mathematical rigorous way to express the potential. I will post a clear comment tomorrow with the link of the explanation 🙂


  49. I've watched this this video before and after I've taken circuit analyses and my understanding of this video is a night and day difference

  50. Ive done the math and measurements for this at my university and youre right. If we measure like you ve said to the end of the video i ve got the right value of voltage. So pe. Lawin its wrong and you are right

  51. Mehdi, Since you have a closed loop against a changing magnetic field, you shall expect every piece of conductive material (not superconductive) in the loop to act as a power supply due to Faraday and lenz law and generate eddy current. Dr. Lewin concludes so because it is so but that doesnt means KVL doesnt hold. it means our persumption on have no voltage difference along a short distance of wire in a closed loop over a changing magnetic field is not holding anymore which is where you are standing on in your video. why the assumption doesnt hold? because of eddy current * neglectible ressitance of the piece is not equal to zero. super conductive materials may act differently. I would like to see an experiment with those in this regard if you happend to have access to some.

  52. i think that this poor old (dutch?) guy got even more shocks in his life than you, but this would proof that there's still hope for you to get old

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