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1. ### I Walter Lewin paradox

I don't remember if I ever said that, and if I did say that was an inaccurate statement, I apologize, I meant of course that if the leads of a voltmeter are disturbed by the induced electric field from changing magnetic field, it cannot be accurate measures the scalar potential between two...
2. ### I Walter Lewin paradox

I don't understand what you are trying to discuss or prove. Isn't the definition of the conservative field potential that does not vary with the path and the voltage that varies with the path already clear? Anyone can use them according to their needs. Do you think that electrical engineers...
3. ### I Walter Lewin paradox

## \text {Because}~~PD_{ab}=PD_{ac}+PD_{cd}+PD_{db} ~ ,~ PD{cd} = PD_{ab}- PD_{ac}-PD_{db}## ##\text{where PD = Potential Difference}## ##Since ~~PD_{ab}, PD_{ac},PD_{db}~~ \text {are known,}~ PD{cd}~~ \text {can be determined.}## Since the electric field in the space outside the ring circuit...
4. ### I Walter Lewin paradox

As someone who graduated from electronic engineering and has been working in related work for decades, I never think that Kirchhoff's circuit laws are wrong. I think only improper application can lead to different results than the actual situation. I don't know if there have historically been...
5. ### I Walter Lewin paradox

So it is not inconsistent with Ohm's law, because the current and power loss in a resistor is calculated in terms of the voltage , not potential difference. But when it is different from the case of electrostatic field, we have to change the expression from j=c*Ec to j=c*(Ec+Ei), where j =...
6. ### I Walter Lewin paradox

I sincerely believe this. (I mean I belive that Prof. Lewin was perfectly aware of what he was doing. He was certainly not confused by the result.)
7. ### I Walter Lewin paradox

Only In the case of an electrostatic field, the voltage is equal to the potential difference. Due to the conservative nature of the static field, the voltage does not depend on the integration path between any two points. In the case of time-varying electromagnetic fields, voltage and potential...
8. ### I Walter Lewin paradox

The thick blue line outside is a section of the ring circuit, and the thick red line is the lead wire of the voltmeter pressed into a T shape. Both are conductors, so charges accumulate on their surfaces to cancel the induced electric field. Since the induced electric fields inside them are...
9. ### I Walter Lewin paradox

The test method used by @mabilde is undoubtedly correct. Single-turn transformers and multi-turn transformer work exactly the same. There is a scalar potential difference between any two points on the transformer winding wires. This not limited to the open circuit output of the two endpoints...
10. ### I Walter Lewin paradox

I think the test method used by mabilde is correct. When we measure voltage with a voltmeter, the DUT has to supply energy, so the Lewin circuit has to supply energy, so the voltmeter loop has to somehow let the changing magnetic flux through to get the energy, otherwise it won't be able to...
11. ### I Walter Lewin paradox

Yes, because a resistor is connected in series, then the potential energy does not increase, and the energy supplied by the induced electric field is immediately lost on the resistor, but if the resistor is replaced by a capacitor, the charge stored in the capacitor will increase, and the...
12. ### I Walter Lewin paradox

For those interested, you can refer to the video link I added in #12 of this discussion thread. I personally think that watching it from 33 minutes will be the most exciting part, but this may not let you understand the whole interesting story. Frankly, I don't really understand some of the...
13. ### I Walter Lewin paradox

I have to mention again that this treatment of describing the electric fields generated by the charges on the surface of conductors in an electromagnetic induction system, and further analyzing the interaction of the electric fields generated by these charges with the induced electric fields, is...
14. ### I Walter Lewin paradox

You seem to describe the problem in a complicated way. I try to understand it simply. It is to divide a whole into two parts, the first part is the scalar potential and the scalar field, and the second part is the induction field. For example, when a positive test charge moves in the scalar...
15. ### I Walter Lewin paradox

I think I see exactly what you mean. I really admire your insight. You now ask the most central and interesting question about this discussion. I actually started thinking about these things that confuse me a long time ago. I hope I can reply soon but I'm out shopping and lunch right now and...
16. ### I Walter Lewin paradox

Not necessarily the case, tax laws are often violated, so you know from the news, if it is not legal tax avoidance, those people will be convicted and punished.
17. ### I Walter Lewin paradox

I would like to introduce the relevant situation further. Does not violate Ohm's law. It is precisely because the definition of the scalar potential must be obeyed, and Ohm's law must be obeyed at the same time, so the calculation equation of the scalar potential must be ##...
18. ### I Walter Lewin paradox

@tedward Thanks to #29 for the informative and valuable reply, a great comment. I agree with most of the points. But there are still some points that I don't fully agree with. We are now dealing with an electromagnetic induction system, and we assume that its total electric field is the result...
19. ### I Walter Lewin paradox

Lewin demo/paradox and general ordinary transformers are electromagnetic induction systems, so the working principle is basically the same. Haven't the common transformers we use every day already shown that a voltmeter can be used to measure scalar potential in such systems? Even though it is...
20. ### I Walter Lewin paradox

In an electromagnetic induction system, when current flows through a impedance, a voltage and corresponding electric field is generated. As for this voltage, or the approximate potential difference when the frequency is very low and tends to zero, it is difficult to say whether it can be...
21. ### B Decompose the E field into conservative and non-conservative parts

Similarly, in the following equation, if the charge distribution and current are constant or change very slowly, all the electric fields generated by the charges can be approximately described by the conservative fields ##~-\nabla ~ \theta~##, and the term ##-\frac {\partial A} {\partial t}##...
22. ### B Decompose the E field into conservative and non-conservative parts

The description of example 10.12 (https://web.mit.edu/6.013_book/www/chapter10/10.1.html) may be considered wrong, because the induced electric field is generally a time-varying field, so all other electric fields correspondingly generated in the system are time-varying, it cannot be accurately...
23. ### Why is there electric field outside a battery?

When I first started doing electronic engineering decades ago, a guru told me not to complicate things by studying electric fields, just remember one formula, which is Ohm's Law. Of course, I don't completely agree with him.
24. ### Current through Flat Sheet or plate

It is also worth noting that in the actual environment, the part with large current will heat up, so the resistance will increase, and the current distribution will also change accordingly, so the final current distribution may be related to power, temperature, heat dissipation and time.
25. ### Am vs Fm variable capacitor receiver, what is the difference?

Regardless of the modulation method, it has a certain bandwidth, so a tuned circuit is needed to selectively receive signals within this bandwidth range, and the most basic form of this circuit is an LC resonant circuit, even an antenna can be regarded as It is an LC circuit, adjusting C can...
26. ### B Decompose the E field into conservative and non-conservative parts

I'm not trying to prove anything in this discussion thread, I'm just describing a concept and a simple calculation method. If people question or even thinks this is wrong, I'll try to explain it. I should also mention about that the so-called build-up of charge on the surface of the wire...
27. ### B Decompose the E field into conservative and non-conservative parts

Thanks for the link, Example 10.12 demonstrates how to use good mathematical techniques to derive analytical solutions to physics problems. Below I try to find potential and potential difference using the simple concept I've been talking about. It is to regard the entire cylindrical structure...
28. ### B Decompose the E field into conservative and non-conservative parts

Thank you for your replies, I think I need some time now to sort out and think about related issues.
29. ### B Decompose the E field into conservative and non-conservative parts

This is just to find out the current, voltage and the amount of charge on the capacitor . I mean find out the electric field in all the surrounding space. The electric field in the entire space includes the induced electric field generated by the inductor and the electric field generated by the...
30. ### B Decompose the E field into conservative and non-conservative parts

simple question. In the following system, due to the induced electric field generated by the inductance, there must be only one electric field, which is a non-conservative field. But how could there possibly be a faster and easier way to find an approximation of this non-conservative field...
31. ### B Decompose the E field into conservative and non-conservative parts

Some references for the surface charge of current-carrying conductors. Includes a demonstration of an electric field that actually exists in the surrounding space outside a current-carrying conductor. https://physicsteacher.blog/tag/surface-charges-on-current-carrying-conductor/...
32. ### I Questions about a Conductor in an Electric Field

The question posed by the OP is now clearly explained graphically, the remaining question that may be asked is what is the net force acting on the conductor? Will it stay still, move left, or move right?
33. ### I Questions about a Conductor in an Electric Field

What I mean of course is that when both the electric field and the conductor extend to infinity, the electric fields in all spaces A, B, and D have no change after adding the conductor. The electric field in space C inside an ideal conductor is always zero, so it doesn't change either. If the...

35. ### I Questions about a Conductor in an Electric Field

From the sketch below, it can be seen that after the conductor is added, the electric field in all spaces does not change, and of course the electric field inside the conductor is also zero.
36. ### I Deriving expression for resistance in terms of current density

You are right, I accidentally wrote the equation wrong.
37. ### I Deriving expression for resistance in terms of current density

A very useful equation is shown here $$V_1-V_2=IR_{12}-\varepsilon _{12}~~~~~\Rightarrow ~~~~~V_1-V_2=IR_{12}-\int_1^2~dl\cdot~E^{'}$$ That is to say, the voltage difference in a circuit with EMF is not equal to IR, but equal to IR minus EMF. This is actually an equation very familiar and...
38. ### I Deriving expression for resistance in terms of current density

My personal opinion as follow.
39. ### I Deriving expression for resistance in terms of current density

I think this equation is reasonable and I don't see any problem with it.

42. ### Engineering Maximum modulation factor of a two tone signal

As far as I know, the maximum modulation factor of Traditional Amplitude Modulation should be 1. When the modulation factor >1, the transmitted wave will be distorted, so that the signal wave cannot be exactly reproduced. This is independent of whether the modulating signal is is single tone or...
43. ### B A universe with only space and time but no mass?

Please don't blame my friend too much. As I have already said, my friend does not even have the most basic concepts of physics, nor has he formally studied philosophy. In fact, I think there are many such people in this world. Their emotional intelligence is well developed, and they like...
44. ### B Decompose the E field into conservative and non-conservative parts

I didn't study this article carefully before, but now I understand that one of the key points is as follows. Equation 22 describes the induced electric field strength, which is constant at every point throughout the ring, and Equation 23 describes the electric potential, whose value increases...
45. ### B Decompose the E field into conservative and non-conservative parts

You are right, now I also think there is something wrong with this equation, I don’t understand either
46. ### B Decompose the E field into conservative and non-conservative parts

This is a physical phenomenon. Whether it is useful or has practical use depends on each individual's opinion and situation. I respect your opinion even if you say it's completely useless, but I don't understand what you mean by extortion.
47. ### B Decompose the E field into conservative and non-conservative parts

Sorry, I really don't understand why this is going wrong. This constant means that when the angle is 0, V can be any value. This is a boundary condition and the user may decide to substitute any value.
48. ### B Decompose the E field into conservative and non-conservative parts

The following example explicitly shows the presence of a scalar field generated in the circuit. Note that the direction of the circular induced electric field is at right angles to the direction of the wires connected to the voltmeter, so the induced electric field does not generate any emf on...
49. ### B Decompose the E field into conservative and non-conservative parts

@vanhees71 I'm not trying to describe the non-existent potential created by the induced electric field, but the scalar field created by the accumulated charge on this circuit. As is the case in this paper http://kirkmcd.princeton.edu/examples/lewin.pdf , the same circuits are also described...
50. ### B Decompose the E field into conservative and non-conservative parts

Since I marked both top and bottom as 0.25V, this already shows that the length of the resistor is assumed to be infinitely small, and the electric field inside the resistor becomes infinite, but the voltage of the resistor is still a fixed value. If I draw that resistor too small, it will be...