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Author Topic: Professor Walter Lewin's Non-conservative Fields Experiment  (Read 253065 times)

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Gibbs,

Your value of .25 for measurements 1 & 3 indicate you are using the sector area of the circular changing flux?

If so, you do know that would require portions of the metering loop to not be normal to the loop but normal to the field lines?

Even so, I would think your measurement would show .5V as opposed to .25V. Why? Because the rest of the secondary is also being measured by the same meter. The voltage of that remaining section would be .75V and opposite polarity to the section you intended to measure (.25V) so the actual displayed voltage would e .5V.

Since I would have figured all of the meter circuit being normal to the secondary loop.... I would calculate using the area of the segment, not the sector.

That would mean the calculated induced voltage of that segment area would be .090845V. That leaves .909155V for the remainder of the secondary loop also being measured with reverse polarity.

.909155 - .090845 = .81831V to be displayed on the meter. Now, move one meter lead back to where we originally decided the measured voltage would be .4V.
We now know another way to find the measured value of .4V  :D

It was easier seeing it as angles in my head  :o


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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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Possible explanation: The V3-V123 measurement has the same amount of flux, but through twice the surface area compared to the V1-V123 measurement?

Very Plausible!

Wouldn't that be an odd thing to miss in basic induction formulae? I don't recall if it is there or not?
-----

Never mind.

It is there. Increasing the area of the loop would decrease the coupling coefficient - perhaps to half in this case?



---------------------------
"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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Measurement V3-V123 is precisely 1/2 the voltage of V1-V123.

Possible explanation: The V3-V123 measurement has the same amount of flux, but through twice the surface area compared to the V1-V123 measurement?


The explanation only works if WW is correct that it looses coupling as the area goes up.  If you make Lewin's secondary bigger, it would still induce total 1V, right?  The fact that it precisely 1/2 shows that there is an exact mathematics relationship in my opinion.  I calculate mine based on 3 dimensional visualization of field lines.  Maybe my 3D is not precise, I'll think about it. 

 
   

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The explanation only works if WW is correct that it looses coupling as the area goes up.  If you make Lewin's secondary bigger, it would still induce total 1V, right?  The fact that it precisely 1/2 shows that there is an exact mathematics relationship in my opinion.  I calculate mine based on 3 dimensional visualization of field lines.  Maybe my 3D is not precise, I'll think about it. 

 

Gibbs,

I'm sure I'm correct about the coupling coefficient. That alone should not change the peak voltage induced. I suspect it only makes the peak 1V for the complete loop more difficult to display due to the weaker coupling and subsequent stronger effect of self-loading (closed loop).

Yes, making Lewin's loop larger should still create the same induced 1V.
The same goes for primary not centered in the secondary loop. There should be no change in induced voltage.


---------------------------
"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...
Yes, making Lewin's loop larger should still create the same induced 1V.
The same goes for primary not centered in the secondary loop. There should be no change in induced voltage.

I ignored my gut instinct when I came up with my numbers for Gibbs' loop. I should have went with it.

WW, I am 99% certain that the induced emf will NOT be 1V with a larger loop. I will prove that tonight if I have the time.
   
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Gibbs,

I'm sure I'm correct about the coupling coefficient. That alone should not change the peak voltage induced. I suspect it only makes the peak 1V for the complete loop more difficult to display due to the weaker coupling and subsequent stronger effect of self-loading (closed loop).


Yes, making Lewin's loop larger should still create the same induced 1V.
The same goes for primary not centered in the secondary loop. There should be no change in induced voltage.

I think you're right about coupling losses and it will change the peak voltage.  This is the issue Ex. and Poynt talked about magnetic field going back in the same loop making it have less inductance.  

I've revised my 3D.  As the field line move outward from the primary, it also has a downward component.  These downward field lines failed to pass the loop surface area reducing the voltage of the total loop and the measured segment.  


   

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I ignored my gut instinct when I came up with my numbers for Gibbs' loop. I should have went with it.

WW, I am 99% certain that the induced emf will NOT be 1V with a larger loop. I will prove that tonight if I have the time.

Now THAT would be interesting  :o

Could it be that the 1:9 ratio changes with the amount of power induced into the secondary?  ^-^

Strange things may happen on loosely coupled transformers  O0


---------------------------
"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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As the field line move outward from the primary, it also has a downward component.  These downward field lines failed to pass the loop surface area reducing the voltage of the total loop and the measured segment.  

So, your thoughts are that each loop sector may not see the same polarity or intensity of the changing flux at each instant during the change?

This can be true in the real world but only on very loosely coupled arrangements like antenna elements, air core RF coupling transformers, etc.

I think many conventional transformers have the primary wound over the secondary or the magnetic loops are tightly closed to avoid this when it is a problem.


---------------------------
"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 think many conventional transformers have the primary wound over the secondary or the magnetic loops are tightly closed to avoid this when it is a problem.


Right, but now we stretch the secondary out so it departs from being tight.  How much did we loose?  I think it's proportional to the distance outward.  Maybe this could explain why magnetic strength is inverse cubed.  Radiate outward is inverse squared and downward component makes it inverse cubed. 

   

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Radiate outward is inverse squared and downward component makes it inverse cubed. 

Interesting. I've never thought of it that way.


---------------------------
"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...
Now THAT would be interesting  :o

Okee.

I performed an experiment to test my hypothesis that the induced emf will decrease as the diameter of the circular loop increases. Here are the test results:

- loop diameter ~ solenoid diameter: emf= 400mV
- loop diameter ~ 2x solenoid diameter: emf=300mV

Summary: The induced emf decreases as a function of loop radius. In my test, doubling the loop diameter resulted in a 25% decrease in emf.

The equations out there support this result.

That explains the results as measured on Gibbs' rectangular loop. The induced emf in that case decreased even more because of the rectangular shape of the loop. I know you guys are going to ask why  >:-)

 O0
   
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Bravo Zulu Poynt,

Your "take one for the team" measuring things is appreciated.

So why does the induced emf decreased even more?  lol

   

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It's not as complicated as it may seem...
So why does the induced emf decreased even more?  lol

You're not going to give it a try? How about an educated guess?
   
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Well, the area of double diameter loop is sure greater than double square.  Unless the loss function is non linear, the square should have less.

   
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...
I performed an experiment to test my hypothesis that the induced emf will decrease as the diameter of the circular loop increases.
...

Not a question of principle. The induced emf is the same but the limits of a real setup disturb the measurement. For example the equivalent circuit of a small coil probe weakly coupled to the loop (due to the gap of diameters) shows an inductance in series, which represents the not coupled inductance part of the loop. With the capacitive coupling between turns, the series resistances, the capacitive impedance of the probes of the voltmeter or oscilloscope, all these effects decreases the measured voltage.

   

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Not a question of principle. The induced emf is the same but the limits of a real setup disturb the measurement.

I agree with the above statement from Ex.

I think the change in the coupling coefficient explains the lower energy transfer ability of the loop because the loop is now more loosely coupled.

The change in coupling coefficient should only change the efficiency of energy transfer between primary and secondary, not the emf.

In practice, we should find that relocating the primary anywhere within the secondary or changing the relative areas has no effect upon the induced emf until other factors become more important in the experiment.

Any variation of the original experiment, like this, simply opens a can of worms.  Normally, this is a great thing in scientific experiments. You must tag and classify each worm  :D
« Last Edit: 2012-04-05, 11:05:11 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...
I agree with the above statement from Ex.
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.

Quote
I think the change in the coupling coefficient explains the lower energy transfer ability of the loop because the loop is now more loosely coupled.
I don't think the physical coupling between the primary and secondary (outside the solenoid) has any real affect on the induced emf. We know that the magnetic field outside the solenoid is practically zero.

Quote
In practice, we should find that relocating the primary anywhere within the secondary
Yes, for the most part this is the case.

Quote
or changing the relative areas has no effect upon the induced emf until other factors become more important in the experiment.
Evidently, not. And the equations disagree as well.

Quote
Any variation of the original experiment, like this, simply opens a can of worms.
Not at all. The results would simply be shifted down in relative amplitude. Everything else is the same.
   

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Poynt,

I'm sure you know your equations but I must ask, which ones?

"I don't think the physical coupling between the primary and secondary (outside the solenoid) has any real affect on the induced emf."

Agreed. That isn't what I meant. Up to the point where other outside factors have an overriding effect, the total loop area change or coupling will not change the induced electric field. The amount of bi-directional power that may be transferred via that coupling does change.


---------------------------
"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...
A total loop area change implies a change in the path outside the solenoid. A larger area implies a net path farther from the solenoid, correct?

Therefore, an increase in area will decrease the induced emf.

I will post the equation later. I have to fight my way to work through 6 inches of wet snow that fell last night (and still falling).  >:(
« Last Edit: 2012-04-05, 13:05:09 by poynt99 »
   
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A total loop area change implies a change in the path outside the solenoid. A larger area implies a net path farther from the solenoid, correct?

Therefore, an increase in area will decrease the induced emf.

I will post the equation later. I have to fight my way to work through 6 inches of wet snow that fell last night (and still falling).  >:(


Are you referring to the circumference of the loop?  If so I think I know what the cause of the result. 

Hope you're on time to work.

   

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

Area and radius of the loop.

What's your theory?
   
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This is what I see.

As the area approaches infinity, the voltage induced is 0. 




   

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It's not as complicated as it may seem...
What are we looking at there Gibbs?
   
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What are we looking at there Gibbs?



Well, if the field lines go up the primary and come back though the loop, the total flux would be less, hence the induced voltage.  I could have overestimate this effect.

 
   

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It's not as complicated as it may seem...
What are the red rings in your diagram representing?
   
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