I have been, and I have to admit I'm quite perplexed with it. In particular equation 35 doesn't seem correct to me. For example, if we assume a point in time where I = 1mA, R1 = 100ohm, R2 = 900ohm, R = 1Mohm and I1 ≈ 0 (as he states) then he seems to be saying 0V = -1V. If someone can help clear this up for me I'd appreciate it.
[Edit 1: fix typos]
I agree equation 35 does not look correct, maybe it is a typo. He seems to have left out the EMF term.
Int E•dl in the wires is 0V (no E fields in perfect conductors, or next to none in real conductors in which case we approximate to 0) and in the resistor is equivalent to I*R (if not then what do you think the contribution of Int E•dl through the resistor is?).
Faradays law? ... Maybe? From your blog BTW:
Your response contradicts several of the things McDonald says in his paper, namely that the voltmeter will read 0V (not 0.125V) and that I1 = 0 is misleading/incorrect. So now who should I believe, you or McDonald?
Anybody else wanna take a crack at this?
I do not contradict with McDonald. You do. I will repeat again what he says: "the result Vmeter = 0 is appealing in that we might naïvely expect the “voltage drop” to be zero between points along a good/perfect conductor." He even shows equation (34) how to calculate voltage between a-b points.
That is Faraday's law yes, how would you use it to calculate the contribution of the line integral of E•dl through the resistor?
You said "Voltmeter shall show 0.125V."
McDonald said "the result Vmeter = 0 ..."
That is Faraday's law yes, how would you use it to calculate the contribution of the line integral of E•dl through the resistor?
Why you suddenly introduce resistor here? We talk about Maxwell's equations and Faradays law. Note that wire segment a-b does not contain any resistor.
QuoteYou said "Voltmeter shall show 0.125V."
Yes. I demonstrated you how to calculate voltage between a-b in case angle is 45 degrees. McDonald provides only formula, not actual calculation. Where's your problem to understand that?QuoteMcDonald said "the result Vmeter = 0 ..."
If you cannot comprehend that McDonald says that it is naïve to expect that voltmeter will show 0V, then our discussion is finished here and now. When you confirm that you can read - we may continue.
I didn't suddenly introduce it. It's inside one of the path integrals in equation 35 which is what I've been talking with you about for these past several posts. I now see that you were still referring to the arc a-b and using equation 34 when you said "Oh, my... You use Ohms law to claim that voltage between a-b is 1V? "
I'm fully able to plug the same numbers into equation 34 as you are. You keep responding to my questions about equation 35 with equation 34.
I have been talking about equation 35 for these past several posts and it's now clear that you've been ignoring them and persisting at talking about equation 34. We're not even talking about the same thing.
"our discussion is finished here and now"
Sounds good to me.
To not repeat a certain arrangement i will also answer this for both definitions of voltage:
A) For definition "Voltage is the integral of all forces pushing on electrons along a given path connecting two points":
The inductors L2 L3 L4 L5 have zero voltage across them at all times (Zero resistance). Any EMF voltage induced in the wire by the magnetic field is instantly countered by the charge separation of electrons.
B) For definition "Voltage is the difference in charge density between two points" (This is what real life voltmeters show)
The inductors L2 L3 L4 L5 have a voltage drop that sums up to the same voltage as the total voltage drop on the resistors. This voltage in the wire is caused by charge separation pushing electrons towards one end of a wire, resulting in more electrons on one end hence higher voltage on one end.
Where does definition B come from? Charge density and Voltage don't even have the same units. [C/m3] vs [J/C]
I disagree. You can split the total mutual inductance M of the loop into two strings of as many inductors as you want in spice. The value you measure in spice will not be the actual scalar voltage potential between the ends of the resistors (which is approximately zero as measured by the voltmeter). Lumping can't be done in this kind of circuit in spice without creating false outcomes.
I see now that you're trying to model the mutual inductance of the "outer loop" i.e. the path formed by the two measurement loops, but not going through R1 and R2. You've arranged the coupling dots in a way that the inner inductors and outer inductors cancel each other out in a way that satisfies there being no flux coupling in the two measurement loops.
I disagree with the thread title.
Walter Lewin used to be a master. Then he started flinging poo at good people.
So i vote we take Master status from him.
A mark of distinction of those who criticize Lewin is their utter and declared inability to teach Maxwell.
Is it still OK to use a voltmeter? Or is every measurement suspect now?
Is it still OK to use a voltmeter? Or is every measurement suspect now?
To be fair, he did issue an apology video. Don't know if it's already been linked to here.
Is it still OK to use a voltmeter? Or is every measurement suspect now?
Those meter measurements were always suspect in certain situations.
Is it still OK to use a voltmeter?
Or is every measurement suspect now?
Regarding McDonalds 'paper' (has that been published on a peer reviewed paper?), let me quote this comment George Hnatiuk from a youtube discussionQuoteI found several errors in the "Lewin's Circuit Paradox" paper back in June to which I alerted Dirk and company and the paper has since been edited with NEW errors introduced and some of the older ones still present. It is very sloppy work at best and nothing I would expect from a university staff member.
As I said before, you should try to analyze how the lumped circuit simplifications come about before tackling non-lumped circuits like Lewin's ring.
Ok. Fair enough. Nobody's perfect. That's why peer review practice is so important and McDonald do error corrections. Could you provide (link to) Dr.Lewin's paper regarding subject, supposedly peer-reviewed?
As I said - when you read McDonald's paper you will see that Dr.Lewin's circuit can be analyzed as circuit of lumped elements. If you disagree, then prove opposite - tell where and how McDonald is wrong.
In the inner loop of Dr.Lewin's experiment E fields can be expressed as E = E.coloumb + E.induced. Wire loop is responsible for E.induced, we can say it is EMF source. As resistance of the wire is very small compared to resistors we ignore it so all the E.coloumb field is located in the resistors - those are load.
Why, it's Romer's paper - it's funny you did not realize it
QuoteAs I said - when you read McDonald's paper you will see that Dr.Lewin's circuit can be analyzed as circuit of lumped elements. If you disagree, then prove opposite - tell where and how McDonald is wrong.
Maybe you are misunderstanding McDonald as well.
E_coulomb kills E_induced in the wires
Romer's paper is about the very same experiment made by Lewin, and it reaches the very same conclusions.
So, since real life voltmeters have (to my knowledge) no way to tell the E_coulomb and the E_induced apart but only see the effect of the resulting total field, it makes little sense to ascribe to the [difference in the values of the] scalar potential any meaning besides that of the voltage measured along a very special class of paths.
And he didn't start with "Hello, hello, hello!" as well. Then they must have found completely different results.
What I see is that they both find that the voltage is dependent on the path, and that when placed on the outside of the loop the voltmeters - applied to the very same two points - give different and opposite phase reading.
Quote"what's the summary field (integral E.dl ) of the loop E = E.coloumb + E.induced?" You did not gave clear answer. Is it zero or not?Here's the answer, assuming that with 'summary' you mean circulation along the circuit's path: the circulation of E_total (integral of (E_coloumb + E_induced) . dl along the circuit's path is equal to minus the time derivative of the flux of B linked by said path.
Yes, it's Faraday's law.
Please do yourself and anybody else a favor: get hold of a copy of "Fields and Waves in Communication Electronics" by Ramo, Whinnery and VanDuzer and read the first four pages of chapter 4 (The electromagnetics of circuits)...
To be fair, he did issue an apology video. Don't know if it's already been linked to here.
Yes it was mentioned here "many pages of posts" ago. Dr.Lewin is one of greatest physics teachers known, he deserves all the titles received.
Punishment shall be proportionate. MIT may revoke his emeritus title, harassed women may seek justice in the court, but come on - removing all his life's work, his courses and lectures from all MIT teaching platforms is way too much. MIT punished not only Dr.Lewin but many, many students. Luckily we have youtube and hopefully social justice warriors of MIT will not do anything about it. We shall not burn scientist with all his books/works/videos just because he made some mistake in his life.
Was he involved in some sexual scandal or something?