Register to reply

Fringe effect

by cscott
Tags: effect, fringe
Share this thread:
cscott
#1
Feb15-06, 06:16 PM
P: 786
A north pole and south pole are seperated by some distance (positioned vertically).

Using the discrete version of Ampere's law:

Take a path rectangle with one vertical side completely inside the magnetic field and the other vertical side completely outside the magnetic field.

Where h = height:
[tex]Bh = -\left[(B_{||}\Delta l)_{top} + (B_{||}\Delta l)_{bottom}\right][/tex]

So there is a magnetic field outside the line of the magnets' edge because the RHS doesn't equal 0? Why is the RHS negative?
Phys.Org News Partner Science news on Phys.org
Sapphire talk enlivens guesswork over iPhone 6
Geneticists offer clues to better rice, tomato crops
UConn makes 3-D copies of antique instrument parts
berkeman
#2
Feb15-06, 07:05 PM
Mentor
berkeman's Avatar
P: 40,659
Since there's no such thing as a magnetic monopole, I assume that you mean there is a bar magnet at the origin with its north pole pointing up and the south pole pointing down. What does it mean when you say "completely outside the magnetic field"? That would be out at infinity?
cscott
#3
Feb15-06, 07:48 PM
P: 786
Quote Quote by berkeman
Since there's no such thing as a magnetic monopole, I assume that you mean there is a bar magnet at the origin with its north pole pointing up and the south pole pointing down. What does it mean when you say "completely outside the magnetic field"? That would be out at infinity?
I meant the north end of a bar magnet pointing down with another bar magnet some distance below it with it's south pole pointing upwards.

I guess by outside of the magnetic field they mean away from the edge of the magnets and the fringe effect. The way I described my rectangular path is the hint they gave in the textbook. "Bh" is the vertical side inside the field, and the term for the other vertical side disappears because B = 0.

berkeman
#4
Feb15-06, 10:43 PM
Mentor
berkeman's Avatar
P: 40,659
Fringe effect

Quote Quote by cscott
I meant the north end of a bar magnet pointing down with another bar magnet some distance below it with it's south pole pointing upwards.

I guess by outside of the magnetic field they mean away from the edge of the magnets and the fringe effect. The way I described my rectangular path is the hint they gave in the textbook. "Bh" is the vertical side inside the field, and the term for the other vertical side disappears because B = 0.
So there are two bar magnets in series. Even so, the B field does not go to zero for that system except at infinity or with ideal magnetic field shielding. Something is missing here....

BTW, the "fringe effect" comes into play when you are working with calculating the capacitance of a finite size capacitor, not some magnetic geometry, IMO.


Register to reply

Related Discussions
Reducing fringe effect, measuring values Electrical Engineering 6
What causes fields to fringe? Classical Physics 11
Decoherence - why does the fringe disappear? Quantum Physics 11
Beyond the fringe General Discussion 4
What is fringe shift? Introductory Physics Homework 1