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Author Topic: Professor Walter Lewin's Non-conservative Fields Experiment  (Read 253083 times)

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Sorry Gibbs. That concept isn't in line with my thinking.

Without changing the circuit we can make the scope register various voltages and either polarity simply by changing the position of the scope relative to the loop.


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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...
Please review the following 3 diagrams.

Are we in agreement with the scope reading in each?
   

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No.

I disagree with the second and third pictures.

All three would register .4V


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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...
No.

I disagree with the second and third pictures.

All three would register .4V

Harvey, are you in agreement with all 3 diagrams?
   
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Yea, but what would the measured voltage be if the scope and leads were directly below the loop?  :D

I'll give you one guess  ;)

(without disconnecting the scope probe from its current points)

If the move is completely symmetrical, then the results are the same.

Because of the geometry of the leads, any induced value in them can more than likely be dismissed as being within the margin of error. Three sides of the lead loop are parallel to the changing magnetic field and thus produce no emf. The circuit under consideration makes up the fourth side. Even if there were some angular offset, we must consider that the distance indicated for the horizontal portion of those leads is 9 times that of the circuit loop. That places the flux value at about 0.0123 times (1/x²) that which the circuit loop experiences which is nearly negligible by comparison even if the entire probe loop were perfectly perpendicular.

Apply Lenz's Law to those probe leads to see that the magnetic field is not affecting the signal within the leads.
  ;)

   

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

Are you in agreement with Harvey on his response regarding the measurement taken from below vs. above?
   

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Yes. It seems I'm asking the easy questions  :)

I'll stop, now. It doesn't become interesting until the metering circuit is no longer normal to the plane of the loop under measurement.


---------------------------
"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...
The 'above' and the 'below' measurements will be opposite sine and offset from mid-point (.5V)

You may wish to review this in light of your last post?
   
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Harvey, are you in agreement with all 3 diagrams?

Yes, that does seem correct from my point of view - the labels at the resistors is a bit odd, but I suppose you needed some moniker for your leads attachment.

It is important to state that those pictures represent a single snapshot in time where the potential is at its maximum.

In essence we have presented here what Professor Lewin demonstrated at the end of his video with the dual probe readings.

 8)

   
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Here is another way to see the problem:



In the same manner that the displacement currents are added to Kirchhoff's current law so that it still applies, we see that the hidden induced emf generators must also be added to Kirchhoff's voltage law in order for it to work. In the present case, it is easy: the "observer" is the voltmeter and we want only know what it measures. But if we had several embedded loops with different induced emf due to varying B fields through each one, I presume that the problem would become very complicated because observer dependent. The Faraday's law is more general and more physical so imho it is the best one to deal with such problems.

   

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It's not as complicated as it may seem...
Yes, that does seem correct from my point of view - the labels at the resistors is a bit odd, but I suppose you needed some moniker for your leads attachment.
1 and 1' for the 100 Ohm, and 9 and 9' for the 900 Ohm. I expected the association to be somewhat obvious, and precludes the need to see the diagram to know which resistor is being measured while referring to these designators.

Quote
It is important to state that those pictures represent a single snapshot in time where the potential is at its maximum.
Of course. Has this ever NOT been the case while discussing this experiment?

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In essence we have presented here what Professor Lewin demonstrated at the end of his video with the dual probe readings.
I disagree. Lewin never makes a measurement with the probe leads normal to the loop. All the diagrams I've posted recently show the probe leads normal to the loop being measured.

In light of the above, you may wish to review those 3 diagrams again and reconsider your agreement with them.
   

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It's not as complicated as it may seem...
No.

I disagree with the second and third pictures.

All three would register .4V

Yes, that does seem correct from my point of view [snip]

You two are in disagreement regarding the 3 diagrams and their associated indicated voltages. Once you two resolve this disagreement, we can move on.
   

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You may wish to review this in light of your last post?

I'll expand upon it.

The meter will display the same above or below, when normal to the measured loop. The sum is zero because the measurements below must be subtracted since the viewpoint of the meter is opposite.

This is a sticking point for many as it boils down to translating the observation. I can't say I agree with the practice but that is the method taught to me and it works.


---------------------------
"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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You two are in disagreement regarding the 3 diagrams and their associated indicated voltages. Once you two resolve this disagreement, we can move on.

No change here.

The perspective of the observing meter doesn't change (Farday). The wire resistance is a minor factor so there is no Ohmic change (Ohm).

Moving the meter lead connections doesn't change the area crossed by B since the meter leads are normal to the loop in all three instances.

I disagree this experiment represents the one by Lewin except both are prime examples of the important differences between EMF and PD (Potential Difference).





---------------------------
"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'll expand upon it.

The meter will display the same above or below, when normal to the measured loop. The sum is zero because the measurements below must be subtracted since the viewpoint of the meter is opposite.

This is a sticking point for many as it boils down to translating the observation. I can't say I agree with the practice but that is the method taught to me and it works.
Why are you "summing" them? The measurement is "as it is". It has one value when the measurement device is decoupled from the experiment, as it is in these two cases, i.e. "above" and "below".
   

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It's not as complicated as it may seem...
No change here.

The perspective of the observing meter doesn't change (Farday). The wire resistance is a minor factor so there is no Ohmic change (Ohm).

Moving the meter lead connections doesn't change the area crossed by B since the meter leads are normal to the loop in all three instances.
In effect what you are saying then if you disagree with the indicated readings, is the following:

1mA x 900 Ohms = 0.4V and
1mA x 100 Ohms = 0.4V

Are you sure you want to stick with your theory?
   
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OK guys,

I think we're making this harder than it really is.  I think that professor Lewin  actually put the probes near the resistors on each side as diagram 2 and 3.  Regarding the angle whether is is normal or not makes no different in the reading although it contains some induction point of view.  

Even if we tell him all this, he probably still laugh at us. IMO


   
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It is true that the actual experiment was reduced by a factor of 10, so that instead of 1V we saw 0.1V overall induced voltage.

Also, it is true that Lewin did not need to have his reference and signal leads separated, nor did he have a need to place them six feet away vertically - however the image attached does show the scope probes being nearly normal to loop and positioned at a point in the magnetic field that little influence would be on them.

 8)
   

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It's not as complicated as it may seem...
It is true that the actual experiment was reduced by a factor of 10, so that instead of 1V we saw 0.1V overall induced voltage.
For the sake of keeping in line with the values Lewin uses on the board, do you mind if we stick to his numbers? The proportions are identical.

Quote
Also, it is true that Lewin did not need to have his reference and signal leads separated, nor did he have a need to place them six feet away vertically - however the image attached does show the scope probes being nearly normal to loop and positioned at a point in the magnetic field that little influence would be on them.
Lewin probably has the probes directly across the resistors; I stated this at the beginning of the discussions on this a year or so ago.

The probes in Lewin's demonstration are highly coupled to the experiment. This is supported by the fact that he illustrates the probes and scope being to the side of the loop, laterally out from the resistor. So there is no question that the probes are largely parallel to the plane of the loop. This is in contrast to the measurements I am discussion right now.

Had you actually performed this experiment, you should be aware that the length of scope wire that has to be parallel to the plane of the loop in order to be coupled to the experiment, only has to be long enough to span the resistor. The probe used by Lewin would have satisfied this case. And also there are 2 or 3 inches of acrylic sheeting around the solenoid supporting the probes in a horizontal position.

Now having said that, are you in agreement with the 3 diagrams and the associated voltages indicated on the scope, are you in agreement with WW, or perhaps you have your own set of values?
« Last Edit: 2012-02-25, 20:37:01 by poynt99 »
   
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The probes are nearly vertical, normal to the time-changing magnetic field.

You may want to review the image attached to my previous post.

It is my contention that do to the manner in which the probes are setup in Lewin's experiment (vertical - normal), no appreciable signal is induced in the probe loops by the time-changing magnetic field. Therefore, the probes are only measuring the voltage drop across the resistors.

Whether or not his probes were AC coupled or DC coupled is not stated (or  I missed it) but either way they are physically connected for a certainty. The probes are not magnetically coupled in this experiment and they are purposely configured so as not to be.

As far as you drawings, I think I already stated that they looked correct to me.

As far as any perceived disagreement between my statements or WaveWatcher's statements, each stand as stated and I see no need to argue our individual understandings.

My statements are based on the empirical proof provided by Professor Lewin and the associated laws that support that proof as formerly stated.

I think its time that you state what you think you have learned from your tests and evaluation and how they measure up to your 3 drawings.  O0
   

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It's not as complicated as it may seem...
The probes are nearly vertical, normal to the time-changing magnetic field.

You may want to review the image attached to my previous post.
You are mistaken. Please review the image I've attached. You meant to say "parallel" vs. "normal" I think.

Quote
It is my contention that do to the manner in which the probes are setup in Lewin's experiment (vertical - normal), no appreciable signal is induced in the probe loops by the time-changing magnetic field.
This is not correct.

Quote
Whether or not his probes were AC coupled or DC coupled is not stated (or  I missed it) but either way they are physically connected for a certainty. The probes are not magnetically coupled in this experiment and they are purposely configured so as not to be.
No one is arguing if the probes are connected or not, of course they are.

You can't know for certain that Lewin was purposely trying to decouple the probes from the experiment. I can tell you from experience however, that he was not.

Quote
As far as you drawings, I think I already stated that they looked correct to me.

As far as any perceived disagreement between my statements or WaveWatcher's statements, each stand as stated and I see no need to argue our individual understandings.
Obviously, at least one of you is incorrect on the matter.

Quote
My statements are based on the empirical proof provided by Professor Lewin and the associated laws that support that proof as formerly stated.
Lewin's setup and results are what they are, but they are being misinterpreted in more ways than one.

Quote
I think its time that you state what you think you have learned from your tests and evaluation and how they measure up to your 3 drawings.  O0
We are getting there, but we're not yet on the same page.
   

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The probes are nearly vertical, normal to the time-changing magnetic field.

Just for clarity, my recent discussion here is based upon the recent drawings by .99, not Lewin's demonstration.

Quote
I think its time that you state what you think you have learned from your tests and evaluation and how they measure up to your 3 drawings.  O0

If debate is thought to be required then that debate should happen between the bench and the experimenter. I may be wrong since Ohm's law is said to always prevail and I've never performed the experiment exactly as pictured by .99. Neither has Lewin, AFAIK.
 


---------------------------
"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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@Poynt99
Quote
Lewin's setup and results are what they are, but they are being misinterpreted in more ways than one.

I would agree, maybe a simple analogy is in order.
In the picture posted there are two pumps, one a point source in which the pump and the restrictions determine the flow and pressure measured at any given point in the system. We should understand that in pump 1 any measure is solely dependant on the pressure and flow through pump 1 itself.

Next we have pump 2, now we can imagine that if we rapidly rotate the whole of the ring filled with water CCW then every single drop of the water in the closed pipe will experience an equal force which will produce a pressure differential across any restriction. If we could imagine that each restriction dissipates energy in proportion to the flow through it not unlike a resistance then some things should become apparent.

First there is no point source and that every single drop of water in the pipe is in itself a source. That R1 is the greatest resistance and due to it's resistance will become a partial source in and of itself by restricting flow which will act on the rest of the system. This is not a normal series loop like pump 1 because the resistance of R1 will create a pressure gradient, a gradient of force, acting in both directions towards R2 thus the standard series calculations have no application. In pump 2, R1 high acts towards R2 low and R1 low acts towards R2 high. The primary focus of pressure is at R1 acting outwards and the primary focus of flow at R2 acting inwards.

It is obvious the two systems are not the same and do not act the same because in pump 2 we have "relative motion" to consider which tends to lead to all kinds of confusion. The concepts are easy however one must have a firm grasp on the mechanics of dynamic systems with relative properties.

Regards
AC
« Last Edit: 2012-02-26, 15:39:54 by allcanadian »


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"Great minds discuss ideas; average minds discuss events; small minds discuss people." - Eleanor Roosevelt.

Be careful when you blindly follow the Masses... sometimes the "M" is silent.
   

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It's not as complicated as it may seem...
Just for clarity, my recent discussion here is based upon the recent drawings by .99, not Lewin's demonstration.

If debate is thought to be required then that debate should happen between the bench and the experimenter. I may be wrong since Ohm's law is said to always prevail and I've never performed the experiment exactly as pictured by .99. Neither has Lewin, AFAIK.

With reference to the 3 diagrams and their associated indicated voltage readings on the oscilloscope, they are correct.

There is an induced emf of 1V, so we know (and will measure) that the voltages across the two resistors has to be +.9 and -.1.
   

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With reference to the 3 diagrams and their associated indicated voltage readings on the oscilloscope, they are correct.

There is an induced emf of 1V, so we know (and will measure) that the voltages across the two resistors has to be +.9 and -.1.

Have you proven that by experiment?

The meter only measures what is at the meter terminals not at the probe.


---------------------------
"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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