Lewin's NCF Experiment and Lecture

[poynt99]

This topic is regarding Walter Lewin's hotly debated non-conservative fields experiment and lecture, where he professes Kirchhoff no longer holds whenever Faraday induction is involved.

A solenoid coil producing a uniform B field, around which is placed a simple circuit with a 100 Ohm and 900 Ohm resistor on opposite sides of the solenoid. This circuit essentially forms a secondary for the solenoid. The solenoid is energized by a step from 0 to some DC voltage, large enough to produce an emf of about 1V in the secondary (1mA).

Scope probes are placed across points D and A as shown, and the voltages across them captured on screen. The resulting peak voltages are as Lewin demonstrates, i.e. -100mV (R1) and 900mV (R2).

[edited to fix "Walter's" name.]

[poynt99]

So we are talking about a circuit such as below,where the solenoid has a 1 volt potential placed across it,where the magnetic field is coming out from the page,and the 100R and 900R make a completed loop around the outside of the solenoid coil--but not connected to the solenoid coil?.

Yes, but the input voltage is whatever is required to induce about 1V on the secondary (1mA flow).

If so,i still do not see how he could have 900mV measured on one side,and 100mV measured on the other side,when both sides of each resistor are joined by a common wire-or the resistors wire it self.

The measurement is correct. There is only one current in the circuit, agreed? Therefore the potential difference across each of the resistors must be different.

The two voltage potentials should still be the same value,and same polarity

Again, looking at the current in the circuit is key. Follow the loop arrows around and see what values and polarities you end up with.

Maybe it is the electric field he is measuring?,but even then,how do you get a difference in potential across a piece of wire that short.

Is it a potential difference across the wires, or an induced emf?

[poynt99]

The previous diagram may be perplexing to some, but the following one should make sense.

Do they both make sense? Why or why not?

[poynt99]

What voltage will the left meter indicate?

[tinman]

The previous diagram may be perplexing to some, but the following one should make sense.

Do they both make sense? Why or why not?

If we look at the moded diagram below,you can see i have placed both a blue line between the bottoms of the resistors,and a red line between the two tops of the resistors.
There should be no voltage drop(or a very extremely small amount)between the points of either the red line,or the blue line. This means that the voltage should be the same for both scope positions marked on the diagram.

I think the problem here lies within the measurement device leads them self-circled in red,where they set up there own loop that the electric field from the solenoid acts upon.
CH1,and CH2 should read the same.
Just my thoughts.

Brad