Eddy Currents (1 Viewer)

[QZP]

You can determine the direction of eddy currents according to Lenz's law.
E.g. If a metal sheet is losing flux into the page, it will experience induced eddy currents in a clockwise direction to replace it.

However, this doesn't make sense to me logically. :S Consider a straight current-carrying wire. It has equal flux on either side of it's length. Now warp it into a circle (to simulate eddy currents). It should have equal flux on both outside and inside the the circle. Thus, in the above example, the eddy currents ARE NOT replacing the lost flux into the page, as it is also producing EQUAL flux out of the page (which "cancels" the other flux into the page).

 

[anomalousdecay]

You situation is just saying that a magnetic object is producing the field around it. Changing the shape of the object just changes its magnetic flux density and the magnetic field lines.

You are confusing yourself.

You have to do work before an induce current can be made.

For example, if you are moving a magnet near a conductor, the work you are doing is providing a magnetic flux which is changing onto the conductor. Hence, the conductor will induce a current as a result of the energy from the flux.

 

[QZP]

You situation is just saying that a magnetic object is producing the field around it. Changing the shape of the object just changes its magnetic flux density and the magnetic field lines.

You are confusing yourself.

You have to do work before an induce current can be made.

For example, if you are moving a magnet near a conductor, the work you are doing is providing a magnetic flux which is changing onto the conductor. Hence, the conductor will induce a current as a result of the energy from the flux.

I have no idea what you just said...
My problem lies in clockwise vs anticlockwise eddy currents not how they are made.

 

[gwilymprice]

What are you actually asking about?

 

[QZP]

I'll simplify it:
A metal sheet is losing flux into the page. Thus, eddy currents are induced per Faraday's law. These eddy currents are circular and CLOCKWISE. This is due to Lenz's Law; the circular eddy currents counteract the changing flux (loss of flux into the page) by creating flux into the page. But my logic tells me even although it is creating flux into the page, it is equally creating flux out of the page, hence the eddy currents do not achieve the purpose of replacing the lost flux into the page.

 

[anomalousdecay]

I have no idea what you just said...
My problem lies in clockwise vs anticlockwise eddy currents not how they are made.

I was explaining how eddy currents are produced as an application of Lenz's Law.

Ok. So you are asking how they are produced?

I'll simplify it:
A metal sheet is losing flux into the page. Thus, eddy currents are induced per Faraday's law. These eddy currents are circular and CLOCKWISE. This is due to Lenz's Law; the circular eddy currents counteract the changing flux (loss of flux into the page) by creating flux into the page. But my logic tells me even although it is creating flux into the page, it is equally creating flux out of the page, hence the eddy currents do not achieve the purpose of replacing the lost flux into the page.

You can't really "lose" flux. That is incorrect terminology.

Generally, the flux is either constant or changing.

I still don't get what you mean afterwards.

I'm sorry but maybe a diagram would help us understand why you are thinking of a contradiction.

 

[QZP]

I was explaining how eddy currents are produced as an application of Lenz's Law.

Ok. So you are asking how they are produced?





You can't really "lose" flux. That is incorrect terminology.

Generally, the flux is either constant or changing.

I still don't get what you mean afterwards.

I'm sorry but maybe a diagram would help us understand why you are thinking of a contradiction.

These are my diagrams for clarity

 

[anomalousdecay]

These are my diagrams for clarity
View attachment 29461

Ok thanks. Your step in 1 and 2 are correct. That is how the eddy currents get induced. However, to increase your clarity, you should add extra field lines to the sheet metal.

When zooming into the eddy currents, you're key mistake is that the field is out of the page.

As an application of Lenz's Law, when removing the sheet from the field, currents are induced to prevent a change in flux.

Hence, the metal sheet will have eddy currents induced clockwise, to create a magnetic field into the page on the sheet metal, preventing the change in flux.

At no point whatsoever does a magnetic field coming out of page interact with the sheet metal (that is; it is non-existent).

This is where you got confused.

Hope this helps.

If you don't understand what I said, feel free to keep asking me questions.

 

[QZP]

What do you mean magnetic flux out of the page is non-existent? :S
You can't have eddy currents that produce JUST magnetic flux into the page.

 

[anomalousdecay]

What do you mean magnetic flux out of the page is non-existent? :S
You can't have eddy currents that produce JUST magnetic flux into the page.

I don't know where you are getting a flux out of the page from.

When moving the sheet metal out of the magnetic field, the flux changes.

So the eddy currents will move clockwise to create a new flux for the sheet metal.

 

[QZP]

I don't know where you are getting a flux out of the page from.

When moving the sheet metal out of the magnetic field, the flux changes.

So the eddy currents will move clockwise to create a new flux for the sheet metal.

Eddy currents are electric currents (moving charges). Thus, they will produce circular magnetic field (use your right hand grip rule for direction) which mean both in and out of the page. So the out of the page flux is from the eddy currents...

 

[Fizzy_Cyst]

Easiest way to think about it is that eddy currents flow to minimise change in flux within the interior of a conductor. Consider the eddy currents flowing in a certain direction, they flow such that the change in flux contained within the area of the eddy current is minimised, as this corresponds to the interior of the conductor which is experiencing a change in flux

 

[anomalousdecay]

Easiest way to think about it is that eddy currents flow to minimise change in flux within the interior of a conductor. Consider the eddy currents flowing in a certain direction, they flow such that the change in flux contained within the area of the eddy current is minimised, as this corresponds to the interior of the conductor which is experiencing a change in flux

Yeah this makes sense.

Basically, you are trying to prevent a change in the state of the metal in that particular area.

If the metal is experiencing magnetism, the eddy currents will move in such a way to constantly keep the metal under that experience of magnetism, preventing a change in its state (and hence preventing that change in flux).