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Author Topic: Professor Walter Lewin's Non-conservative Fields Experiment  (Read 253060 times)
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What are the red rings in your diagram representing?

Uh... the secondary loops.

   

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It's not as complicated as it may seem...
OK, I see where you're going, and that I'll need to explain things...tomorrow.

Going to the last hockey game of the year for the Oilers tonight with me pops.  O0
   

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OK, I see where you're going, and that I'll need to explain things...tomorrow.

Going to the last hockey game of the year for the Oilers tonight with me pops.  O0

Nothing better than that!


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"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   

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Uh... the secondary loops.

Separate but concentric secondary loops  :)

Faraday via Maxwell: "The line integral of the electric field around a closed loop is equal to the negative of the rate of change of the magnetic flux through the area enclosed by the loop."
With concentric secondaries the rate of change is equal on all sectors. Gibbs's red circles will each have the same induced emf because all sectors of these loops are normal to the changing magnetic flux.

On the rectangular secondary there is a decrease in induced emf, not because the area of the loop has changed but because not all of the secondary conductor is normal to the changing magnetic flux. If you distort that rectangular secondary into a nice round loop, the same amount of emf will be induced as each of the above two red circles.

Here is where we get into trouble by considering 'potential differences' between any two points around the secondary'.
AND - Where we run into the contradiction  :D

That is my take on it!








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"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   
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I'm not really certain I understand 100% what Ex is saying. However, I will say that my method of measurement has no serious affect on the theoretical induced emf. And the equations clearly indicate that the induced emf IS different at differing diameters.
...

What equations?
The induced emf depends only on dphi/dt through the circuit surface, it doesn't depend on the surface, therefore it doesn't depend on the diameter.

Show us an experimental setup giving a result depending on the diameter, and I could say where is the bias. For example if you use a big loop around a solenoid, of course the emf will depend on the diameter if you don't increase simultaneously the length of the solenoid.

   

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What equations?
The induced emf depends only on dphi/dt through the circuit surface, it doesn't depend on the surface, therefore it doesn't depend on the diameter.

Show us an experimental setup giving a result depending on the diameter, and I could say where is the bias. For example if you use a big loop around a solenoid, of course the emf will depend on the diameter if you don't increase simultaneously the length of the solenoid.

Even with an infinitely-long solenoid, the induced emf decreases as a function of increasing loop radius.

I will elaborate shortly.
   
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Calm down guys,

It's a good time to review your thinking.  What other possibilities did you or Poynt missed.  I have one other possibility in my mind.  Either way, I'm excited to hear. 

   

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It's not as complicated as it may seem...
Please, speak your mind Gibbs. What possibility do you have in mind....and in what regard?
   
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Please, speak your mind Gibbs. What possibility do you have in mind....and in what regard?


I don't think it is right, that's why I rather hear you.  We may have measured a fixed resistance, that's all. 



   

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It's not as complicated as it may seem...
Not quite sure what you mean Gibbs. We use fixed resistors, yes.

Why could a fixed resistance be a problem here?
   
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Let's say we have 1000 Ohms .  The total induced voltage is 1 V , so .1 ma go through.  If we measured 100Ohms, the voltage is .1V .  If we makes the loop larger, more wire resistance is added.  The total loop amp go down.  If we measured  100Ohms as before, the voltage would indicate less.  However, this scenario doesn't fit well.  

I just thought of another possibility and the calculation matches.  The pic below shown how you made your measurement.

   

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I've have found that my earlier statement about sections of the rectangular loop effecting induced emf, while still true, isn't enough to explain the observations stated by others.

Rather, the act of measuring 123-3, just like the measurements on the circular secondary, splits the surface of induction into two surfaces. These two induction areas will be of opposite polarity. The induced emf into the latest secondary should remain 1V. The problem is that the .4V (123-2) is only .4V when it is being measured.

The act of measuring between any two points on similar secondary loops always has an effect upon the reading. Even in the described de-coupled state the metering circuits acts to split the induction area into two.


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"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   

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It's not as complicated as it may seem...
Gibbs,

The wire resistance is miniscule in comparison to the 1000 Ohms total we have. Even moving to a loop of twice the radius (2x the length of wire) will not skew the results by any significant amount.

With reference to your diagram, I didn't measure the emf that way.

Edit: Corrected "100" Ohms to "1000" Ohms.

« Last Edit: 2012-04-07, 13:58:27 by poynt99 »
   

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It's not as complicated as it may seem...
 :o

WW, I'm not sure what you're getting at. But what I could understand (I think), doesn't sound quite right.

Stay tuned, the explanation for all is forthcoming.

.99
   

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Staying tuned  ;D

Basically, I'm still agreeing with Ex.


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"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   

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Buy me some coffee
 Were All Tunered   8)
   

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It's not as complicated as it may seem...
Glad we're all "tuned-up".  ;D

Well, it seems I am going to have to do another experiment with a much longer solenoid to prove my hypothesis.

It was all going well until I became aware that my hypothesis is in conflict with Faraday's law; emf is predicted to be the same, regardless of loop radius. I find that difficult to swallow, since I know that outside the solenoid the electric field drops off as a function of 1/r. And we know that the electric field is what is responsible for the induced emf. The emf being equal to the line integral of the electric field around the conductive loop of interest.

Something doesn't add up. In fact, it would seem that the accepted theory is in conflict with itself.  C.C
   
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Don't take this all by yourself Poynt.  Let us in... We can help.

You did in fact measured a drop in voltage and said to be 1/r.  Can you show me your measured config. for that?  I think Ex was on the right track but I also sense another element that can effect induced voltage, but I can't be sure unless I have more information.

   

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It's not as complicated as it may seem...
Coming up soon Gibbs. I'm working on a detailed diagram which will help explain my hypothesis.
   

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It's not as complicated as it may seem...
I understand now after studying my diagram. It's a simple relationship.

Yes the E field weakens as a function of 1/r from the solenoid, but that is to a single point at the given radius "r" from the axis. As r increases, so does the circumference at that give radius, so when we do the line integral around that larger circumference, the result is the same net E field, which should produce the same net emf.

However, things don't look so well for that rectangular loop, as you will see shortly. I'm fairly certain this explains the weaker than expected emf readings.

.99
   

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Poynt,

From the perspective of the solenoid even the rectangular loop is still circular. The result for the entire loop should still be 1V.

Your thoughts on increased radius being compensated by increased circumference is very logical. That thought has made perfect sense to me in the past but I found it to be the wrong idea.

The only idea that seems to work is consideration of the loop surface area. Not the loop's total surface area... Rather, the loop's surface area covered by the magnetic field only from the inside of the solenoid. So, as long as the secondary is a simple loop (no resistors, no measurements of voltage across segments), the induced voltage will remain at 1V because the surface area effected by the solenoid doesn't change.

I don't think the reduced measured voltage has anything to do with the shape or size of the measured loop having a change in induction. It is the result of the size and shape of the secondary loop causing confusion in locating previously measured points.

Unfortunately, none of the above will make sense unless you understand that any attempt at measurement changes the one secondary loop into two secondary loops.


---------------------------
"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   

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For my argument, I offer the following I posted in another forum some time ago:

Quote
When Lewin made a statement about the metering circuit resistance needing to be a certain level......
It is clear to me he only suggests a high enough resistance so the metering circuit doesn't drag the measured voltage down (overload the loop).

Except for the possibility of a very low resistance meter overloading a poorly coupled secondary, the resistance of the meter has nothing to do with the induced emf on the loop.

If the resistors were of equal value... A to D would have been .5V.

Why?
Because the act of connecting a meter loop across the diameter creates two loops ( with the meter circuit normal to the loop and internal solenoid magnetic field) .

The emf induced into EACH loop would be 1V. BUT, the meter now being connected to BOTH loops causes some confusion. No matter where you connect the meter, you will create a second loop. Doing so, ALWAYS means the meter is measuring both loops at the same time.

The relative connection of the meter (polarity of the meter) is reversed for one loop relative to the other loop.

Therefore, the meter will display a summation of the two applied emf's -   .5V .


The whole Lewin exercise was simply a good demonstration of the prime component of non-conservative fields - Path Dependence.
« Last Edit: 2012-04-08, 13:22:49 by WaveWatcher »


---------------------------
"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   

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It's not as complicated as it may seem...
Poynt,

From the perspective of the solenoid even the rectangular loop is still circular. The result for the entire loop should still be 1V.
Perhaps, but I am not yet convinced. The E field is a circular vector. Any loop shape other than circular is non-ideal.

Quote
Your thoughts on increased radius being compensated by increased circumference is very logical. That thought has made perfect sense to me in the past but I found it to be the wrong idea.
The math supports the idea, and it makes sense to me. You will see the equations in my next posts.

Quote
The only idea that seems to work is consideration of the loop surface area. Not the loop's total surface area... Rather, the loop's surface area covered by the magnetic field only from the inside of the solenoid. So, as long as the secondary is a simple loop (no resistors, no measurements of voltage across segments), the induced voltage will remain at 1V because the surface area effected by the solenoid doesn't change.
The induced voltage is not affected by series resistors nor decoupled measurement leads. That's been proven.

Quote
I don't think the reduced measured voltage has anything to do with the shape or size of the measured loop having a change in induction. It is the result of the size and shape of the secondary loop causing confusion in locating previously measured points.
I disagree. Again, a non-circular loop isn't optimal for induction. My diagram will show why.

Quote
Unfortunately, none of the above will make sense unless you understand that any attempt at measurement changes the one secondary loop into two secondary loops.
I don't understand this concept. Can you think of a test to prove this? The tests I've done to specifically address this issue clearly indicate that the measurement loop is not affected by the experiment. If there is no induction in the measurement loop (which I've proven for myself), and the measurement loop is high impedance (10M), how can it affect the induction loop?
   

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It's not as complicated as it may seem...
Attached is the diagram illustrating a top-down view of the gradient E-field, and other salient points of interest.

I plan on doing some tests with the rectangular loop. One test will be to see if the measured emf between points 0a and 0b is equivalent to that measured between points 0b and 1a. According to the accepted theory, they should be (or not?), but I want to see it myself.

The white circle in the diagram denotes the solenoid perimeter. You see also that the E-field at that area is black (the most intense) and how it diminishes in intensity in both directions away from, and towards the axis.

The red circle is a sample point for calculating the E-field intensity, and for noting the orientation of the E-field wrt the rectangular loop. Towards the right side, it's clear that the diminishing E-field is not inducing much into the loop, as it is almost normal to the loop in that area. It is not until the extreme right of the loop that the E-field is inducing emf, and at that point the E-field is already diminished to 1/2 intensity.

Notice the equation for emf assumes a circular loop.

.99
   
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First, you made me feel bad on art work. lol

Second, it's a good test to perform.  I would add suggestion that we vary the de-coupled length to see what effect it may have on measurement. 

   
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