How to determine the direction of eddy current? (1 Viewer)

[Momentazeus]

Could someone help me out please? I am especially confused for plates moving into magnetic fields

 

[d1zzyohs]

Hey mate;
Do you know the right hand solenoid rule? It's very very useful for eddy currents.
An eddy current will always work to oppose an induced magnetic field; basically,
the plate doesn't want to go into the magnetic field - and it creates a current (and hence a magnetic field to oppose it).

If you think about the velocity vectors in a plate moving into a field; the current direction parallel to the vector should be going the other way.

It's a bit of a convoluted topic.

 

[Momentazeus]

Hey mate;
Do you know the right hand solenoid rule? It's very very useful for eddy currents.
An eddy current will always work to oppose an induced magnetic field; basically,
the plate doesn't want to go into the magnetic field - and it creates a current (and hence a magnetic field to oppose it).

If you think about the velocity vectors in a plate moving into a field; the current direction parallel to the vector should be going the other way.

It's a bit of a convoluted topic.

Wait so how would you apply that to this situation?

 

[d1zzyohs]

Wait so how would you apply that to this situation?
View attachment 36070

Okay; compartmentalise the magnetic field into two halves; one going out of the field, one going in.

The diagram and example I drew up - servers for the right side going in. As you can see; the eddy current is in the opposite vector direction to the movement. On the other half (the left side of the field); we see that the eddy currents are trying to resist letting the disk out of the field.

So; overall - theres a braking effect - as the side going in resists the incoming movement; and the side going out resists the outgoing movement.

 

[tyrone97]

Another better way of figuring this out rather than to try use Lenz's Law is to imagine a test positive charge sitting on the metal disk and apply the Lorentz force law (F=qvB or F = IBL).
The test positive charge is moving to the left when the disk rotates into the magnetic field (so I, the current, points to the left).
The magnetic field points into the page.
Line up your hand accordingly, and you'll see that the force points down the page (this explains why the eddy current goes down for the part that is in the field).

Of course, since charge is conserved and shouldn't pile up anywhere it has to loop around in the part that is outside the magnetic field.