Lewin's NCF Experiment and Lecture

[tinman]

  I'm a bit baffled today, I came across the term "convection current". Then I
  encountered "self capacitance".
    I was just wondering why after seven decades I've all of a sudden taken an
  interest in these things, and I've worked that one out, it's Google!
             John.

Quote: The inter-winding capacitance of a coil is sometimes called self-capacitance,[9] but this is a different phenomenon. It is actually mutual capacitance between the individual turns of the coil and is a form of stray, or parasitic capacitance. This self-capacitance is an important consideration at high frequencies. It changes the impedance of the coil and gives rise to parallel resonance.

[poynt99]

Perhaps a review of my posted result's?,as you seemed to have missed something.

I've missed nothing. I am fully aware that your numbers don't quite add up. We've seen that from the very beginning.

Diagram 1 and associated scope shot has to be inverted in order for us to do our loop measurement points in order.So invert the scope probe position,and invert the scope shot,so as to gain the correct value,which will be negative 400mV.

I think I speak for all here when I say STOP USING THE INVERT SWITCH ON YOUR SCOPE! It is not required 99% of the time and it only confuses the matter.

800mV-400mV-400mV gives us a value of 0 volt's.
But we still have the 100 ohm resistor to measure,and so our total value is not 0 volts.

You apparently don't realize it, but your setup or measurements aren't perfect (which is ok, I doubt mine is either), otherwise all 4 voltages would sum to 0V. I sincerely hope you're not implying that a non-zero sum means Kirchhoff doesn't hold?

Kirchhoff's voltage law is based on the assumption that there is no fluctuating/changing magnetic field linking the closed loop. In our DUT,there is clearly a changing/fluctuating magnetic field linking the loop,and this can be seen in all my scope shot's by the reversing current flow across each measuring point during the decoupled tests-and all the other tests carried out in this thread that i have done.

Quote-KVL is based on the assumption that there is no fluctuating magnetic field linking the closed loop.  In the presence of a changing magnetic field the electric field is not a conservative vector field. Therefore the electric field cannot be the gradient of any potential. That is to say, the line integral of the electric field around the loop is not zero, directly contradicting KVL.

The results of my test,the results of Lewins test,and the definition of KVL indicating that a changing magnetic field linking the closed loop make KVL invalid in this case,seems to all fit together,and Lewins statement is correct.

What have i missed here Poynt?.


Brad

You've gone and googled and drank the coolaid instead of paying close attention and analyzing what I've shown you here.

I am fully aware that the E field is nonconservative, and that Kirchhoff does not apply when generating and measuring the E field. However, Lewin was equating the E field with potential drops across resistors in a circuit and then espousing that Kirchhoff does not hold. It does hold, as you've mostly proved with your measurements. Lewin was clearly mixing the two concepts (potential difference and E field measurements) in an effort to discredit Kirchhoff, but the bottom line is that Kirchhoff holds regardless if the circuit is static (DC), or dynamic (Faraday induction). When the case is dynamic, the DC battery is replaced with an inductance, through which the emf is produced in the circuit, and it is this emf (conveniently not illustrated by Lewin) that is in exact opposition to the potential drops across the resistors, resulting in a zero sum.

[ramset]

Minnie
Don't stop walking ... those little battery scooters that "help" people get around .

they _help_ people Lose all mobility thru atrophy .

Re Google and folks your age , They say you'll become addicted because you weren't raised with it .

Chet

[tinman]

I've missed nothing. I am fully aware that your numbers don't quite add up. We've seen that from the very beginning.

I think I speak for all here when I say STOP USING THE INVERT SWITCH ON YOUR SCOPE! It is not required 99% of the time and it only confuses the matter.

I have not used the invert switch on the scope for any of these measurements--you misunderstood what i was saying. The first scope point/polarity has to be inverted to do our loop test point measurements,as the polarity show is opposite to that needed for a series loop measurement.

I am fully aware that the E field is nonconservative, and that Kirchhoff does not apply when generating and measuring the E field. However, Lewin was equating the E field with potential drops across resistors in a circuit and then espousing that Kirchhoff does not hold. It does hold, as you've mostly proved with your measurements. Lewin was clearly mixing the two concepts (potential difference and E field measurements) in an effort to discredit Kirchhoff, but the bottom line is that Kirchhoff holds regardless if the circuit is static (DC), or dynamic (Faraday induction). When the case is dynamic, the DC battery is replaced with an inductance, through which the emf is produced in the circuit, and it is this emf (conveniently not illustrated by Lewin) that is in exact opposition to the potential drops across the resistors, resulting in a zero sum.

Ah ok,now i see where i was looking in the wrong direction.
Also,would using a longer solenoid coil,and higher value resistor's,enable me to gain more accurate measurements?,as i would like to get this to all work out much closer to correct values to those i have-just to clean up my experiment a bit.

You've gone and googled and drank the coolaid instead of paying close attention and analyzing what I've shown you here.

Well first up,after hearing this saying many times here on this forum,and being Australian--what the hell is coolaid?--im guessing some sort of wonder drink?.
I always search google for information when i dont see what i should be seeing,or to understand something a little better than i do-->is this not what we all do?.

You apparently don't realize it, but your setup or measurements aren't perfect (which is ok, I doubt mine is either), otherwise all 4 voltages would sum to 0V. I sincerely hope you're not implying that a non-zero sum means Kirchhoff doesn't hold?

It would appear that my non-zero sum is due to slight measurement error,and/or the circuit not being quite up to scratch,which left me around 100mV under the total 0 volt result i should have seen-hence my trip down google lane to find the answers


Brad

[Pirate88179]

Brad:

Koolaid is a powdered fruit drink mix that has been a favorite of kids over here since the 60's.

There phrase "Drink the Koolaid" comes from a tragic event where a guy named Jim Jones led a group of folks that he had brainwashed to a place in Guyana and ran the place like a drug crazed dictator.  When a US Senator went there to see if the folks were OK, he was shot and killed.  Jones then instructed his followers that God want them to drink the Koolaid with him.  The Koolaid was loaded with poison and all of them were found dead a few days later.  Everyone in the group followed this nut and did whatever he told them to do including killing themselves.

So, when someone is said to have drunk the Koolaid, it simply means they have blindly accepted and followed something someone else has told them without any reasoning on their own.

Sorry, if the above is not totally clear but, it will give you some idea of the history of this often used phrase.

Bill

PS  Next, we should talk about the phrase "Jump the shark" which comes from a Happy Days tv program episode.