Fun Induction Challenge

[Carl-NC]

The links below are Parts 1 & 2 of an interesting lecture by MIT professor Walter Lewin. In these videos he shows how induction completely violates and renders useless Kirchhoff's Voltage Law:

http://www.youtube.com/watch?v=eqjl-qRy71w
http://www.youtube.com/watch?v=1bUWcy8HwpM

The first link was posted over in the LRL forum by someone who deeply wishes that "mysterious forces" are available to explain ordinary fraud. I watched the second link to see if Prof. Lewin "spilled the beans" and showed there is no mystery, and Kirchhoff is still right. But he continued to present it all as a bunch of nonsense.

We've got some smart folks here, so I thought I'd toss this out to see who can figure out were a Professor Emeritus of MIT completely botched his homework.

- Carl

[Qiaozhi]

The links below are Parts 1 & 2 of an interesting lecture by MIT professor Walter Lewin. In these videos he shows how induction completely violates and renders useless Kirchhoff's Voltage Law:

http://www.youtube.com/watch?v=eqjl-qRy71w
http://www.youtube.com/watch?v=1bUWcy8HwpM

The first link was posted over in the LRL forum by someone who deeply wishes that "mysterious forces" are available to explain ordinary fraud. I watched the second link to see if Prof. Lewin "spilled the beans" and showed there is no mystery, and Kirchhoff is still right. But he continued to present it all as a bunch of nonsense.

We've got some smart folks here, so I thought I'd toss this out to see who can figure out were a Professor Emeritus of MIT completely botched his homework.

- Carl

I need to watch both these lectures again and think about it somewhat (it's after midnight here) ... but I did notice that he makes a calculation error in the 2nd lecture when he states that 10 cm^2 equals 10E-2 m^2. Of course this should be 10E-3 m^2. (10 cm = 0.01m, but not when they're squared).

[Davor]

He was not cheating, but to fully grasp what he meant you should see the lecture note first. Trouble wit his explanation on the blackboard is that he did not actually connect the voltmeters at the very same points A and D, but on the resistors, and then it all makes sense. A wire in between makes all the difference as it is a part of the loop. You may draw the lines between the resistors as coils, and it will be crystal clear to you. The professor just made it a bit more dramatic this way.

So you have flux, in a loop it produces voltage, by the sum of all resistances that voltage produces current, which has a direction - hence voltage drops on resistors. Easy.

[deemon]

He was not cheating, but to fully grasp what he meant you should see the lecture note first. Trouble wit his explanation on the blackboard is that he did not actually connect the voltmeters at the very same points A and D, but on the resistors,

I think that he really did connect the voltmeters exactly to the points A and D . You see , we have 3 loops here in the circuit . The central loop with the magnetic flux changing inside , and two side loops with voltmeters but without the flux . And because of Faraday's law , if the flux don't change in the loop - there must be zero voltage .... but we have a current through the resistors in the side loops ( because of the central loop current ) - 100 Ohm in the left and 900 Ohm in the right . So the voltage drop on those different resistors ( with equal current ) is what the both voltmeters really shows . No mystery of course

[Tepco]

The links below are Parts 1 & 2 of an interesting lecture by MIT professor Walter Lewin. In these videos he shows how induction completely violates and renders useless Kirchhoff's Voltage Law:

http://www.youtube.com/watch?v=eqjl-qRy71w
http://www.youtube.com/watch?v=1bUWcy8HwpM

The first link was posted over in the LRL forum by someone who deeply wishes that "mysterious forces" are available to explain ordinary fraud. I watched the second link to see if Prof. Lewin "spilled the beans" and showed there is no mystery, and Kirchhoff is still right. But he continued to present it all as a bunch of nonsense.

We've got some smart folks here, so I thought I'd toss this out to see who can figure out were a Professor Emeritus of MIT completely botched his homework.

- Carl

Dead wrong, every word and demonstration, even formulas. Pseudoscience\dumbing people at its best. Just dead wrong. Nature not work this way, never did and never will.
Easy to test and judge. Gyu even ignored to mention coil inductance, responsible for stored energy, time needed to ramp it up etc. But this is just fine, compared to what some other people can do. I will just stop here on comments, otherwise 5 more forum pages will be lost.

[Qiaozhi]

Now I've had a chance to watch the videos again, here is my analysis:

The links to these videos were initially posted over on the LRL forums, by someone with very little credibility, as evidence that Ohms Law does not pass a blind test. I presume he meant to say "double blind", but even so the link has nothing to do with double blind testing. Consequently I didn't pay much attention to the video, except to note the interesting mannerisms of the "eccentric professor" that Walter Lewin was trying to portray. Actually I did find him very engaging as a teacher. Many lecturers could learn something from this.

In the first video he shows us a simple potential divider network connected to a 1V battery. No problem there - everything works as advertised, and Kirchoff's Voltage law is not violated. At one point he connects a voltmeter across R2 and shows the voltage to be +0.9V. He then calculates the same voltage across the battery and R1 in series, which is also 0.9V. No problem there. In calculating the voltage across the battery / R1 combination, he calculates the voltage drop across R1 as 0.1V, and subtracts this from the battery voltage to get 1 - 0.1 = 0.9V. However, if you were to measure the voltage across R1 on its own, using the voltmeter, you would need to invert the connections so that the +ve probe is connected to the battery, and the -ve probe is connected to point D. In this case the voltage is +0.1V.

OK - "so what?", I hear you say ...

If we move on to the second circuit:
The battery is removed, and a current is induced into the circuit from an external solenoid. In this case, 1mA is flowing around the loop. This can only happen because the wires connecting R1 and R2 are acting as inductors. So, in effect, the solenoid is acting as the primary, and the secondary is formed by a single loop of wire with a 100R resistor in one side and a 900R resistor at the other side. When the magnetic field from the solenoid is changing, the two resistors are isolated by the inductances of the wiring, and hence the voltages across the two resistors can be different. If the current flowing in the loop has reached steady-state, then the two resistors are in parallel. Although the steady-state condition here means the current is zero, but that's another story. Considering the connecting wires between the two resistors to be an ideal inductance (i.e. no resistance) the voltage across R2 will +0.9V, and the voltage across R1 will be +0.1V ... not -0.1V. Remember that you need to change the polarity of the voltmeter connections for R1.

Another way to look at this would be to leave the +ve terminal of the voltmeter connected to point D for both measurements. In the first circuit - for R2, the -ve probe is connected to point A (where VR2 = 0.9V). For R1, the -ve probe is connected to the +ve terminal of the battery (where VR1 = -0.1V). In the second circuit - for R2, the probe is connected to point A (where VR2 = 0.9V). For the second circuit, the -ve probe is also connected to point A (where VR1 = -0.1V). Hence, you can readily see that both measurements give the same result. There is no discrepancy between Kirchoff and Faraday.

So the Professor Emeritus of MIT botched his homework by not paying closer attention to the sign of the values he was calculating / measuring.

Seeing such a basic error caused me to check the date of the video in case it was posted in April. But I found the posting date to be November 2006, which of course doesn't actually prove anything. Perhaps, in the end, it was a real error and not a prank. But I do find this hard to believe, considering the cock-up over Ohms law in the first video and the other cock-up when converting cm^2 to m^2 in the second video. Also, I cannot imagine several professors from the Physics and EE departments simply accepting these results without investigating further to uncover the error.

Personally I think this must have been a [very clever] prank.

[ivconic]

I written down his name, will discharge him next Monday!
Period!




P.S.
That's what you get from lot of studying and oversimulating!

[Qiaozhi]

Why I believe this was a prank.

http://www.youtube.com/watch?v=97oTDANuZco
He practices every lecture 3 times before presenting it. I'm sure everything was pre-planned to the smallest detail, even the blatant errors such as Ohms Law.

Unlike this guy ->
http://www.youtube.com/watch?v=dsTY7...eature=related

[Aziz]

Unlike this guy ->
http://www.youtube.com/watch?v=dsTY7...eature=related

*LOL* Funny Prof.

"Do it! Do some drawing! Do it! Do it!"
Simply do it!

Aziz

[Mechanic]

HI Guys,

In the last test that he made showing the scope shots, I have a feeling that his scope leads were having current induced into them obscuring the actual measurement that he was trying to make.

Cheers Mick

[deemon]

Guys , it's OK with professor , don't blame him What he told in his lecture is completely according with Faraday's law . You just forget here about one important thing - we have a deal with non-conservative force . So the voltage polarity depends on the direction of the movement along the loop . And another thing - all wires that aren't a part of the loop with changing magnetic flux inside does work only like a conductor , not an inductor . So we can connect two voltmeters to the same two points of the circuit , and they can show different polarities , and that is the thing that Faraday's law describes .

But it's all a "theory" , so let's go to a practice We can easily perform just the same experiment that professor Lewin did , and only what we need here are the good inductor coil with rapidly changing magnetic field , 2 resistors ( let's use the same values - 100 and 900 ohms , just for fun ) , and instead of 2 voltmeters we can use one dual-trace scope . But what about the inductor , where can we get it ? In order to provide a proper shape of magnetic flux we can use a ferrite stick with a coil wound on it , and quite a simple circuit with a pulse generator and high-voltage switch ( mosfet or bipolar ) , that pumps a current to the coil and abruptly shuts it down , providing a very high and short voltage pulse that can move the electrons in our circuit . In another words - we need a PI metal detector with the ferrite antenna . And I have PI detector exactly of this kind - http://www.geotech1.com/forums/showthread.php?t=19273 , why don't use it ? If it can do the job , I can save the time

Here on the photos we can see the pulses on the both sides of the circuit with two equal voltage probes . On the left side we have 100 ohm resistor , and on the right side 900 ohm resistor . And everyone can see that both probes really connected to the same points , and the signals does really have opposite polarity and pulse amplitudes does have ratio approximatelly 1:9 , according to the resistance ratio ..... so I think that professor is completely cleared now

[Aziz]

*LOL*
Does anybody remember the "energy loss in charging a capacitor" - problem? That's funny too.
http://www.smpstech.com/charge.htm

Half the energy has disappeared. Where did it go?

I'll try to find it. Because I have a TEE-degree ("Trial & Error-Engineer"). Particularly when I'm as drunk as a lord.

Cheers,
Aziz

[Altra]

My two cents

In part 1 at about 8:50 secs he draws this equation
VD-Va1 = 0.9v
VA2-VD = 0.1v
= 1.0V

The above he incorrectly eliminates the source voltage (DA)

Kirchoff's Law

VA1 + VA2 - DA = 0

0.1v + 0.9v - 1.0v = 0

Something else in the beginning of part 2 he explains his test set up. He eliminates the resistors and replaces them with power supplys his words "100 volts" and "900 volts" maybe he ment to say 100mV and 900mV. Not enough info to disect his experiment, need a schematic

[Qiaozhi]

Here on the photos we can see the pulses on the both sides of the circuit with two equal voltage probes . On the left side we have 100 ohm resistor , and on the right side 900 ohm resistor . And everyone can see that both probes really connected to the same points , and the signals does really have opposite polarity and pulse amplitudes does have ratio approximatelly 1:9 , according to the resistance ratio ..... so I think that professor is completely cleared now

I'm afraid you've lost me here. If you have two scope probes connected to the same point in the circuit, then you must display the same voltage. Unless one of the channels has its probe set to 10x and is inverted.

What is there in your setup that defines which probe is measuring which resistor? From what I can see from the photos, they truly are connected to the same point. So what gives?

Edit: What happens if you move both scope probes to the same side of the ferrite coil? I suspect you are picking up a signal from the coil directly into the probes.

[deemon]

If you have two scope probes connected to the same point in the circuit, then you must display the same voltage.

Of course it would be so , if we have a "usual" circuit . But now we have a strong magnetic flux piercing our circuit just in the middle , and being the "motor" for the current without any battery . If the electrons being driven counterclockwise around our loop , for example , we'll see a negative charge on the upper lead of the left resistor and at the same time on the lower lead of the right resistor - it explains the opposite polarity on the probes ( or voltmeters ) .

Edit: What happens if you move both scope probes to the same side of the ferrite coil?

They shows the same polarity and voltage , I checked it of course . And the scope itself cannot inverse the pulse because the "inverted" button on the scope panel ( near the channel B input ) wasn't pressed ...