Faraday's Law vs Kirchoff's Rule in circuit - nonconservative fields

Join the discussion
Ask a follow-up here, or get your own question answered by working scientists, mathematicians and engineers — people, not an autocomplete.
Real named experts · corrections over time · the nuance an AI answer skips
2 replies · 6K views
Dens
Messages
74
Reaction score
0
I am trying to compare the "relation" conventions used in Kirchoff's Loop Rule with Faraday's Loop Rule.

Kirchoff

Please go to this MIT OCW link on Kirchoff's Rule and go to page 8/29. Of the four boxes, I would like to point this one

K_E.jpg


Note that the yellow electric field was added by me. This picture also follows the integral

[tex]-\int_{a}^{b} \mathbf{E}\cdot d\mathbf{s} = \int_{a}^{b} -Eds = \Delta V = \varepsilon = -IR[/tex]

Since ds and E are parallel.

Nonconservative Fields with Faraday

Now if I go to this video (I take you to EXACTLY where I want you to watch, so don't worry about searching which part of the video does this happen)

http://www.youtube.com/watch?v=UpO6t00bPb8#t=10m22s

Now quoting him

Now I go through the resistor, so I get +IR, since E and dl are in the same direction, Ohm's Law tells me I get +IR

Note that his circuit arrangement is exactly like mine, he went from a high potential to a low potential. The current, electric field in the wire, and the traveling direction are all the same, yet he gets +IR instead of -IR

is he still using this "E dot dl" [tex]-\int_{a}^{b} \mathbf{E}\cdot d\mathbf{s}= \Delta V[/tex]? How does Faraday's Law apply for non-closed paths? Because it seems like Lewin is using [tex]\int_{a}^{b} \mathbf{E}\cdot d\mathbf{s}= \Delta V[/tex] (no minus sign)

The same confusion goes when he talks about the electric field in the battery.

Could someone please clarify for me? Thank you
 
Physics news on Phys.org
Studiot said:
This subject has already been done to death here at this forum

eg

https://www.physicsforums.com/showthread.php?t=453575

do a forum search for other threads

and also here

http://forum.allaboutcircuits.com/showthread.php?t=16150&highlight=lewin&page=3

Second link wasn't very helpful and I can't pinpoint my answer in the first link because it seems like it derailed into some argument on Lewin's teaching ability.