Eddy currents (1 Viewer)

[The-Exiled]

How do you know which way they "Spin"?

Like, for example:

There is a magentic field coming out of the page and we move a metal surface across to the right?


. . . . . . . . . . . . . .
. . . . . . . . . . . . . .
. . . .____. . . . . . . .
. . . | | . . . . . . .
. . . |____| . . . . . . .
. . . . . . . . . . . . . .
. . . . . . . . . . . . . .
. . . . . . . . . . . . . .
--->


How do you tell which way they spin, I know it's to oppose the force but I don't understand how tell which way, haha

Help please?


Well the diagram come out right, hopefully you know what I'm talking about ^_^

 

[bazookie]

there will only be a eddy current when a part of that metal is outside of the magnetic field. So, with the direction of movement going right, an eddy current will be induced in an anticlockwise motion where it goes down in the part of the metal still within the magnetic field and goes up in the part outside of the magnetic field... i will draw a picture if you do not understand... it is pretty hard to explain

EDIT: by the way, you work it out with the right hand push rule. refer to your text book if you are unfamiliar with this. This rule is pretty important

 

[The-Exiled]

Oh okay, so when lemme get this straight... When it goes off the magnetic field the part of the metal still on the magnetic field the eddy currents go anticlockwise and downwards and the part of the metal off the magnetic field goes anticlockwise and upwards...? is that right?

right hand push rule the one where thumb = current, palm = force and finger pointing forward = magnetic field?

AKA Right hand palm rule? lol

 

[bazookie]

OK, so an emf is induced in an area of changing magnetic flux right? this is basic. In your case, you have a metal sheet and the emf produced here is an eddy current. When an area of the metal is moved from an area inside a magnetic field to an area without, an eddy current is induced due to a change in flux. You can find the direction through a simple application of Lenz's Law and the right hand push rule.

a picture of this can be seen on page 141 of the jacaranda textbook if thats the book you use.

 

[adosh]

can someone please explain this......is a emf induced by a changing magnetic flux( ie cutting flux lines faster or increasing or decreasing strength in magentic flux) or is a emf induced when a conductor just moves in an external magnetic field,,such as say a flat metal sheet,, or a wire moving through magnetic field lines at ocnstant speed...or is it both???????

 

[clonestar]

How do you know which way they "Spin"?

Like, for example:

There is a magentic field coming out of the page and we move a metal surface across to the right?


. . . . . . . . . . . . . .
. . . . . . . . . . . . . .
. . . .____. . . . . . . .
. . . | | . . . . . . .
. . . |____| . . . . . . .
. . . . . . . . . . . . . .
. . . . . . . . . . . . . .
. . . . . . . . . . . . . .
--->


How do you tell which way they spin, I know it's to oppose the force but I don't understand how tell which way, haha

Help please?


Well the diagram come out right, hopefully you know what I'm talking about ^_^

What bazookie said is right..

Use whichever rule you have been taught with force, B and I and realise that eddy currents will only form in region where this is a overlap where lines of flux are cut and then the conductor has no lines of flux cut.

then use FBI rule I use left hand rule and to the right of that conductor the area overlapping there will be B out of page and the force of the thumb opposes the direction so instead of it pointing to the right it points to the left as an application of lenzs law.

Then the current is down the page. The area not exposed to change in flux the current is up the page and this makes a loop which ultimately makes an anticlockwise eddy current.

 

[clonestar]

can someone please explain this......is a emf induced by a changing magnetic flux( ie cutting flux lines faster or increasing or decreasing strength in magentic flux) or is a emf induced when a conductor just moves in an external magnetic field,,such as say a flat metal sheet,, or a wire moving through magnetic field lines at ocnstant speed...or is it both???????

It's both...

a change of flux can be created by moving a magnet into a stationary coil where the change in flux is the moving magnet or a moving coil into a stationary magnet as the coil initiates the change in flux by cutting the lines of force.

 

[adosh]

no no i understnad that much,,,a change of flux by moving te magnet into the coil or vice versa because we are increaseing the mflux lines,,,but im saying this imagine we have a coil or a wire better to use a wire and say a magnetic field is pointing upward and we hold the wire and move it to the right at a constant speed,,,,,,,that is we dont move the wire down or up but just to the right,,is and emf generated