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Author Topic: Lewin's NCF Experiment and Lecture  (Read 45723 times)

wattsup

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Re: Lewin's NCF Experiment and Lecture
« Reply #75 on: April 30, 2016, 05:26:46 PM »
Would slipping a small Faraday cage (Like a can shaped one) over the coil stop it from influencing the probe wires?  It would seem to me this would be the easiest way if it works.
Bill

Actually what would be interesting to see is the following as shown below.

Keep the vertical coil (VC) (orange) and the center positioned loop (blue) but position two metal cones (grey) as shown to see if the impress from the VC to the loop is mainly perpendicular. Then remove the top cone and try again. Then remove the bottom cone and replace the top cone and try again. So what would this show you?

Then relate this to which is the open side of the VC that is then being connected to the discharge. Any relation there?

Then remove the cones and slide the loop 1/4 way up, try it, then near the top, try it, then 1/4 way down from center, try it, then all the way down and try it again. So what would this tell you? Simple little things can say a lot.

You can then compare the same as above but replace the cap discharge with a steady pulse. Now what will be the difference?

wattsup


tinman

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Re: Lewin's NCF Experiment and Lecture
« Reply #76 on: May 01, 2016, 02:06:07 AM »
Ok,below are the test results from the vertical wire test,where the two wires from the measuring points to probe are vertical to that of the resistor loop,and around 1.5 meters high-away from the DUT.
The scope probe and ground are then hooked to the end of these vertical wires-speaker like cable.

Results seem to be much as i expected.


Brad

poynt99

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Re: Lewin's NCF Experiment and Lecture
« Reply #77 on: May 01, 2016, 02:35:14 PM »
Brad.  ;)

When you have a chance, all that is left are the wire segment measurements.

Yes, your prediction of the voltage from D to A was correct.

tinman

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Re: Lewin's NCF Experiment and Lecture
« Reply #78 on: May 01, 2016, 02:54:56 PM »
Brad.  ;)

When you have a chance, all that is left are the wire segment measurements.

Yes, your prediction of the voltage from D to A was correct.

Ah yes-i missed that one Poynt.
Had a busy weekend with kids,grandkids and some work on my 4x4.
Will get it done ASAP-probably tomorrow night.

Brad

poynt99

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Re: Lewin's NCF Experiment and Lecture
« Reply #79 on: May 01, 2016, 03:01:46 PM »
OK Brad, no problem.

What is your prediction for the wire segments?

And sorry, your prediction AND measurement for the voltage across points D and A was/is correct.

tinman

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Re: Lewin's NCF Experiment and Lecture
« Reply #80 on: May 01, 2016, 03:32:35 PM »
OK Brad, no problem.

What is your prediction for the wire segments?

And sorry, your prediction AND measurement for the voltage across points D and A was/is correct.

I believe that it should be 0 as seen it the test with the wires running along side the resistor connector wire,but something is telling me that that will not be the case.

In all this(so far) dose this not make Lewins claim correct?,as we do not have 0 volts across the resistors as Kirchhoff would suggest.

Brad

poynt99

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Re: Lewin's NCF Experiment and Lecture
« Reply #81 on: May 01, 2016, 03:37:17 PM »
I'm not going to give you the answer (I know the answer), just curious what your thoughts were.

Perform the measurement and let's see what it is.

tinman

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Re: Lewin's NCF Experiment and Lecture
« Reply #82 on: May 02, 2016, 03:01:07 PM »
Well oddly enough,i get around 400mV across the bottom wire,and around 400mV across the top wire.

This was with the duel cable going to the scope probe vertical to the resistor loop,as in the other tests.

Why the two are different?-i have no idea,but i carried out the test many times on each wire,and the results were always the same.

Brad

poynt99

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Re: Lewin's NCF Experiment and Lecture
« Reply #83 on: May 02, 2016, 04:59:39 PM »
Well oddly enough,i get around 400mV across the bottom wire,and around 400mV across the top wire.
;) It is not 0V as most would seem to expect/guess.

Quote
Why the two are different?-i have no idea,but i carried out the test many times on each wire,and the results were always the same.

Brad
Do you mean why in the first case the measurement was 0V on each wire segment, and in this last case the sum is close to the calibration emf?

I was hoping you would have put it all together, as you've done quite well so far. Isn't this just a step-down transformer? We have 50 to 100 turns on the primary, and one turn on the secondary, loaded with a resistance of R1+R2.

You are measuring the actual emf induced in the secondary loop because the measurement device is decoupled from the primary (and secondary). That is why the measurements are different.

Now as a final step, use your vertical probe to go around measuring the 4 components (R1-->wire_seg-->R2-->wire_seg) in serial fashion following the current path and write the voltage down for each. If performed correctly, two measurements will be positive and two negative in polarity (the two resistors will be one polarity, and the two wire segments will be the other polarity). Add the 4 values together and you should be left with something close to 0V.

tinman

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Re: Lewin's NCF Experiment and Lecture
« Reply #84 on: May 03, 2016, 01:30:02 AM »
;) It is not 0V as most would seem to expect/guess.
Do you mean why in the first case the measurement was 0V on each wire segment, and in this last case the sum is close to the calibration emf?

I was hoping you would have put it all together, as you've done quite well so far. Isn't this just a step-down transformer? We have 50 to 100 turns on the primary, and one turn on the secondary, loaded with a resistance of R1+R2.

You are measuring the actual emf induced in the secondary loop because the measurement device is decoupled from the primary (and secondary). That is why the measurements are different.

Now as a final step, use your vertical probe to go around measuring the 4 components (R1-->wire_seg-->R2-->wire_seg) in serial fashion following the current path and write the voltage down for each. If performed correctly, two measurements will be positive and two negative in polarity (the two resistors will be one polarity, and the two wire segments will be the other polarity). Add the 4 values together and you should be left with something close to 0V.

Yes,the sum equals 0,but what has that to do with what Lewin claims?.
We can sum up voltages around any circuit to equal 0 if we measure from certain points using certain polarities.

It would seem to me that Lewins claim is correct,when measuring across the two resistors,as the sum is not 0,it is the induced 1volt EMF in this case,being the total across each resistor.
If we have a current flow,then we are not measuring just the E filed,but the EM field.
If it were just the E field,then Kirchhoff law may hold,in that the measuring was carried out incorrectly. But as we also have current flow,and a magnetic field,then it would seem to me that Kirchhoff's law dose not hold in this situation.


Brad

poynt99

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Re: Lewin's NCF Experiment and Lecture
« Reply #85 on: May 03, 2016, 01:53:27 AM »
Yes,the sum equals 0,but what has that to do with what Lewin claims?.
It has everything to do wtih Lewin's claim that Kirchhoff does not hold in this case. In his lecture he is clearly not only comparing apples and oranges, but he is muddling the whole affair entirely.

Quote
We can sum up voltages around any circuit to equal 0 if we measure from certain points using certain polarities.
In other words, if you always ensure your measurement apparatus is decoupled from the DUT, you will not only measure the correct voltages across each component, but you will prove that Kirchhoff holds each and every time. Lewin claims that it does not, and you just proved that it indeed does hold every time.

Quote
It would seem to me that Lewins claim is correct,when measuring across the two resistors,as the sum is not 0,it is the induced 1volt EMF in this case,being the total across each resistor.
If we have a current flow,then we are not measuring just the E filed,but the EM field.
If it were just the E field,then Kirchhoff law may hold,in that the measuring was carried out incorrectly. But as we also have current flow,and a magnetic field,then it would seem to me that Kirchhoff's law dose not hold in this situation.
I can't make much sense out of this last bit. Each statement on its own is either wrong or nonsensical and seems to indicate that you don't understand what you should have just learned.

tinman

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Re: Lewin's NCF Experiment and Lecture
« Reply #86 on: May 03, 2016, 01:43:47 PM »
It has everything to do wtih Lewin's claim that Kirchhoff does not hold in this case. In his lecture he is clearly not only comparing apples and oranges, but he is muddling the whole affair entirely.
In other words, if you always ensure your measurement apparatus is decoupled from the DUT, you will not only measure the correct voltages across each component, but you will prove that Kirchhoff holds each and every time. Lewin claims that it does not, and you just proved that it indeed does hold every time.
I can't make much sense out of this last bit. Each statement on its own is either wrong or nonsensical and seems to indicate that you don't understand what you should have just learned.

Perhaps a review of my posted result's?,as you seemed to have missed something.

Diagram 1 and associated scope shot has to be inverted in order for us to do our loop measurement points in order.So invert the scope probe position,and invert the scope shot,so as to gain the correct value,which will be negative 400mV.

Diagram 2(which is the correct polarity) and associated scope shot,shows us the potential across the 1k resistor. We can safely say that it is close to 800mV.

Diagram 3(which is the correct polarity) and associated scope shot,again shows us a value that is close to negative 400mV.

800mV-400mV-400mV gives us a value of 0 volt's.
But we still have the 100 ohm resistor to measure,and so our total value is not 0 volts.

Kirchhoff's voltage law is based on the assumption that there is no fluctuating/changing magnetic field linking the closed loop. In our DUT,there is clearly a changing/fluctuating magnetic field linking the loop,and this can be seen in all my scope shot's by the reversing current flow across each measuring point during the decoupled tests-and all the other tests carried out in this thread that i have done.

Quote-KVL is based on the assumption that there is no fluctuating magnetic field linking the closed loop.  In the presence of a changing magnetic field the electric field is not a conservative vector field. Therefore the electric field cannot be the gradient of any potential. That is to say, the line integral of the electric field around the loop is not zero, directly contradicting KVL.

The results of my test,the results of Lewins test,and the definition of KVL indicating that a changing magnetic field linking the closed loop make KVL invalid in this case,seems to all fit together,and Lewins statement is correct.

What have i missed here Poynt?.


Brad

minnie

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Re: Lewin's NCF Experiment and Lecture
« Reply #87 on: May 03, 2016, 02:14:33 PM »



  I live on the side of a hill. I set out to shepherd my sheep, go down to the river,
  up to the windmill and then go home. When I get home I'm at the same elevation
  as when I started.
      I can't walk anymore and the kids got me this-

tinman

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Re: Lewin's NCF Experiment and Lecture
« Reply #88 on: May 03, 2016, 02:31:25 PM »


  I live on the side of a hill. I set out to shepherd my sheep, go down to the river,
  up to the windmill and then go home. When I get home I'm at the same elevation
  as when I started.
      I can't walk anymore and the kids got me this-

It's a good thing that there was not a land slide under your house while you were away from home,as then you would have gained more energy going down hill to the river than it took you to get back home :D

The energy form point A to point B and back to point A can change if there is another force acting upon one of those points,or the area between the points.

I drove my boat from my house jetty, down river to my favorite fishing spot,and used 2 liters of fuel.
I drove my boat back to my house jetty from my favorite fishing spot,following the same path,but used 3 liters of fuel on the return trip. ;)

Brad

minnie

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Re: Lewin's NCF Experiment and Lecture
« Reply #89 on: May 03, 2016, 02:31:50 PM »



  I'm a bit baffled today, I came across the term "convection current". Then I
  encountered "self capacitance".
    I was just wondering why after seven decades I've all of a sudden taken an
  interest in these things, and I've worked that one out, it's Google!
             John.