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Author Topic: Professor Walter Lewin's Non-conservative Fields Experiment  (Read 253057 times)

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.99,

In no way are you or your experiment a comparison to Rosemary. I can only imagine what her results would be. Perhaps our disagreement is due to zipons?  >:-)


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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
Good Luck with the Op Darren  O0
   

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Good Luck with the Op Darren  O0

Ditto!


Make sure all holes that should be there - are still there after you wake up.
Be sure no freely moving parts are secured with an accidental stitch! I'm not speaking of them tying your shoes together  :D



---------------------------
"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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Gibbs,

Is it possible that the proximity of the meter to the loop is having an effect on meter performance?

I'm not saying the readings are other than I would expect. Simply, all possible effects should be ruled out.


---------------------------
"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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Gibbs,

Is it possible that the proximity of the meter to the loop is having an effect on meter performance?

I'm not saying the readings are other than I would expect. Simply, all possible effects should be ruled out.


WaveW,

I show you a picture below.  Hope you can see why I think the height matter. 

-----------
Get better soon Poynt

   

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Gibbs,

Yes, I do. You must consider the amount/density and angle of the field lines entering the metering circuit loop and the secondary loop.

Raising the meter increases the number of possible lines entering the metering loop. The value seen will be the sum of the two segments (created at the secondary loop by inserting the measuring circuit) plus any possible induction now occurring in the metering circuit.

Lowering the height to almost zero simply decreases the amount induced into the metering loop. At or near zero height, the sum will be zero because each of the two segments of the secondary loop (again, attaching two meter probes and meter segments the secondary loop into two loops) always have 1V induced, each. Since the current path taken by both segments is the same direction, those current paths meet in the metering circuit and cancel each other to zero.

In your above drawing, there is only one secondary loop segment because the meter loop is at an extreme edge of the secondary rectangle. If that rectangle was a circle there will always be two segments created by attaching the meter circuit.


The height does matter to the observer but doesn't matter to the measured loop. Please be aware that the height will 'seem' to matter to the measured loop but only because the metering loop has a direct effect upon what it displays depending upon the meter's relation to the measured loop and the percent of field lines seen from the source solenoid.

Once the meter is high enough to register a voltage you should be able to change the perpendicular angle to a lower number and see further measured voltage change, both plus and minus.

I hope that is clear enough.



---------------------------
"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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Gibbs,

Yes, I do. You must consider the amount/density and angle of the field lines entering the metering circuit loop and the secondary loop.

Raising the meter increases the number of possible lines entering the metering loop. The value seen will be the sum of the two segments (created at the secondary loop by inserting the measuring circuit) plus any possible induction now occurring in the metering circuit.

Lowering the height to almost zero simply decreases the amount induced into the metering loop. At or near zero height, the sum will be zero because each of the two segments of the secondary loop (again, attaching two meter probes and meter segments the secondary loop into two loops) always have 1V induced, each. Since the current path taken by both segments is the same direction, those current paths meet in the metering circuit and cancel each other to zero.

In your above drawing, there is only one secondary loop segment because the meter loop is at an extreme edge of the secondary rectangle. If that rectangle was a circle there will always be two segments created by attaching the meter circuit.


The height does matter to the observer but doesn't matter to the measured loop. Please be aware that the height will 'seem' to matter to the measured loop but only because the metering loop has a direct effect upon what it displays depending upon the meter's relation to the measured loop and the percent of field lines seen from the source solenoid.

Once the meter is high enough to register a voltage you should be able to change the perpendicular angle to a lower number and see further measured voltage change, both plus and minus.

I hope that is clear enough.



WaveW,

I find it is easier to apply KVL to get the meter reading.  Let's pick the metering loop through that segment .

dB/dt(meter) + V (meter) + V(segment) = 0

dB/dt(meter) is the induction due to field lines.  This depends on the height of the decoupling. 
V(meter) is the voltage register on the meter
V(segment) is just the current x resistance of the segment

Simple, don't you think?
   

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Yes  :D

In some cases KVL provides the same answers. There is where I disagree with using KVL. The potentials you measure only exist when the meter is connected.

The only accurate way to measure between any two points on this loop is to place the meter in the center with probes extending to the inside of the diameter and across the diameter.

Don't be surprised if the results are all zero. There are no real potentials on the loop.


---------------------------
"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 don't know if I agree that the induced E field has no effect on a point charge. If it did not, induction would not work.

As far as verifying experimentally the 1/r effect at a point, I don't need to, do I?

"If it did not, induction would not work": this is the main point to verify. This objection is logical and I have already tried to verify it.

If the induced E field has an effect on a point charge, then it has also an effect on charges in a small circuit not encircling the varying flux.

To test it, I have used a toroid coil. On one side, near the toroid, I put two large metallic cylinders acting as capacitors.
They were placed at some distance from each other and a wire connected the two capacitors with a voltmeter in series. All was placed in order that there is the presumed emf in the wire. But no voltage was measured.
I have put an inductance in series with the wire to make the circuit more sensitive because resonant at the frequency used to power the toroid coil. Same null result.

A voltage was measured only when the wire was placed through the toroid hole and the two capacitors at each end were near enough from each other. In this case I consider that the circuit was looped thanks to the displacement currents between the two capacitors.

Note that if this effect of E=-dA/dt on a single charge was real, its corollary is that the reversed effect would also be possible, and so, we could induce an emf in a toroid coil from outside, without any conductor through the hole. I'm not aware that any experiment of this kind gave positive results.
What I observe is the experimental impossibility to show any effect of E=-dA/dt on elements of circuit not encircling the flux and consequently the effect on a single charge is doubtful or too weak to be measured. I don't know (yet) why. This effect is indispensable to test the 1/r effect, otherwise with a closed circuit around the flux, we can only measure the well known trivial emf not depending on r.


   

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

As you don't approve of the last proposed test, I have another to run past you. The goal here of course is to introduce a measurement technique that can non-intrusively determine if the addition of two decoupled test leads skews the actual induced emf.

The idea; use a current probe (Rogowski coil, toroid, etc) to determine the induced current, with and without the decoupled leads attached.

What say you?
   

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I like the idea of a no-core Rogowski coil.
I would expect the current measured to be the same anywhere on the loop. I am quite sure KCL holds unless there is a fair amount of inductance somewhere on the loop. Well, KCL will hold regardless. If such an inductance value existed their would be signs of phase shift.

I'm using a 2-section solenoid so metering leads may be in-plane but perpendicular to the magnetic field. So far, any two measured points result in zero, just as I think it should. We'll see when I don't need my daughters to hold the experiment during the test  :-X


---------------------------
"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 take that as an approval then.

So, two tests: measure the loop current with and without the decoupled leads attached. Either the current will be the same in both cases, or not. If they are the same, do you agree the decoupled measurement method is valid?
   

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Valid?

As in reflecting the voltage between the probe tips -or- voltage measurement created just by connecting the meter?

If is the latter then, yes.

They aren't the same.

1. Reducing or eliminating inductive coupling on the metering circuit is only part of the problem.
2. Using current readings and Ohm's law to determine potential drop between two points is only straightforward with conservative fields.


---------------------------
"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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With the Rogowski coil (with no core) some of what I'm saying should be clarified.

I think it would be interesting to measure current at each resistor, separately, with the metering circuit in the so-called 'decoupled' position but with probes at opposite sides of the diameter (original points A & D).



---------------------------
"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...
Valid?

As in reflecting the voltage between the probe tips -or- voltage measurement created just by connecting the meter?
Neither.

Perhaps it will be helpful if I try to restate the problem/challenge:

First, I am going to assume that you agree that an emf will be induced in the loop, agreed?

Second, it is my understanding that you assert that the TRUE induced level of loop emf is being skewed by the application of two decoupled measurement leads placed anywhere on the loop.

Do you concur with my understanding of your objection?
   

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It's not as complicated as it may seem...
As current probes might be just as susceptible to "influence" by the experiment, I have yet another option for you to consider WW:

Make the induction loop, a second measurement loop. Or put another way, change from two resistors to one, and make it a 1k value. So we have a wire loop that goes 357º around the solenoid, and the loop is loaded with a single 1k resistor (which makes up the last 3º of rotation).  This second measurement loop does the integration essentially around the entire solenoid, giving us a pretty accurate reading of the induced emf.

Now, after we note what the total induced emf is by this method, we introduce our two decoupled leads once again across any two random points on the loop and observe if the emf value measured by the "second measurement loop" as described above has changed any appreciable amount.

If there is little or no change, then can we say that the decoupled measurement method is valid, i.e. non-intrusive to the experiment?
   

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Neither.

Perhaps it will be helpful if I try to restate the problem/challenge:

First, I am going to assume that you agree that an emf will be induced in the loop, agreed?

Yes.

Quote
Second, it is my understanding that you assert that the TRUE induced level of loop emf is being skewed by the application of two decoupled measurement leads placed anywhere on the loop.

Do you concur with my understanding of your objection?


I can't concur with that statement. The actual emf induced into each of the loop segments created by connecting your metering circuit will still equal 1V.

.....

Wait a minute... (Just saw your follow-up post)

What is wrong with leaving the loop under test as is and measuring current at both resistors while the voltage metering circuit segments the loop under test?

Have you already done so and found that the resistor currents aren't equal?

KCl will hold but only for the circuit being observed.


357o or 360o doesn't matter. The same emf is induced into the loop because it is closed by a resistor. The skewing I mentioned is related to current balance between two segments of the same loop.

The emf induced into a second separate loop is determined by the surface area bounded by that loop, not by the surface area bounded by the other loop.

  

I think we are still speaking separate languages.


---------------------------
"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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Gentlemen,

Correct me if I'm wrong but is the issue about the meter when connect to the loop change the amount of current flowing through the resistors?

If I understand correctly, the only way it could "stripped" some current from the main loop is current flowing through the probes, KCL... right?  How about insert a low value cap in series with the probes? 

-----------------

Poynt, hope you're doing better. Welcome back.
   

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Gibbs,

The input impedance of the meter means the meter isn't dragging current of any appreciable amount.

I don't know how to state the real issue any more plainly than - connecting the metering circuit segments the area of induction of the secondary loop into two areas of induction.
Where these two areas of induction meet, in the meter circuit, the current paths are opposing one another.

It is as simple as looking down upon the loop and the metering loop while connected. Decoupling means absolutely nothing except to minimize errors caused by unwanted induction.

The area of induction is what matters with the discussion, not the loop except that it defines the area of induction.



---------------------------
"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 can't concur with that statement. The actual emf induced into each of the loop segments created by connecting your metering circuit will still equal 1V.
Then I think you are still most likely the only one that understands what you really mean WW. I would suggest you succinctly state what the problem is, and what the effect of that problem is.

Quote
Wait a minute... (Just saw your follow-up post)

What is wrong with leaving the loop under test as is and measuring current at both resistors while the voltage metering circuit segments the loop under test?

Have you already done so and found that the resistor currents aren't equal?
I think it's rather unlikely that the current at each resistor will or even possibly can be different. With practically zero induction and infinite impedance in the measurements leads, they will not alter the induced emf, nor the induced current in the secondary loop. So no, I have not separately measured the resistor currents. I don't even know how you would propose one do that ???

Quote
The skewing I mentioned is related to current balance between two segments of the same loop.
I want some of what you've been smokin'  8) (esp right now)

Quote
The emf induced into a second separate loop is determined by the surface area bounded by that loop, not by the surface area bounded by the other loop.
Therefore, the measurement loop emf = 0V.

Quote
I think we are still speaking separate languages.
I think the real problem is that we just don't understand what you're getting at.
   

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

Correct me if I'm wrong but is the issue about the meter when connect to the loop change the amount of current flowing through the resistors?
You and I both are struggling to understand. Hopefully WW can clarify his point of view.

Quote
Poynt, hope you're doing better. Welcome back.
Feeling better each day Gibbs, thanks.  ;)
   

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It's not as complicated as it may seem...
I don't know how to state the real issue any more plainly than - connecting the metering circuit segments the area of induction of the secondary loop into two areas of induction.
Where these two areas of induction meet, in the meter circuit, the current paths are opposing one another.
What?  :o

Please explain.  ???
   

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What?  :o

Please explain.  ???

This is the crux of the matter. I do intend to explain. It is going to take more than words.

At this point, I'm thinking the only understandable explanation must include rotatable 3D graphics and a video conference with a live demonstration.

If you find something to smoke that cuts my working hours I'll buy a kilo  :D


---------------------------
"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...
This is the crux of the matter. I do intend to explain. It is going to take more than words.

At this point, I'm thinking the only understandable explanation must include rotatable 3D graphics and a video conference with a live demonstration.

If you find something to smoke that cuts my working hours I'll buy a kilo  :D
A well-annotated diagram usually does the trick WW. I'd encourage you to give it a shot.
   
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I think the only way to settle this is to see who understand how the system works. 

I posted a problem below.

The total induced emf is 1V
Scope reading position in-plane reads .2V
R1 = 1 Ohm
Find R2. 

   
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