Electromagnetic Braking, unit 4.

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That's what I get.

Post pictures of the questions. Try the snipping tool or print screen and paint.

Simple.

Edited, should see the question now

Thanks! To clear things up...

The discs motion and the magnetic field is perpendicular to the rotation of the disc, so there is a change of magnetic flux linkage , so an emf is induced such that to oppose the motion creating it. The Emf then leads to the force opposing the discs motion due to the Flemmings right hand rule.

Kind of hard to imagine, but how exactly is the disc cutting this magnetic field in the coil of wire? Is it in that small region only?

No.

Think of it like this. Initially there are 0 magnetic field lines passing through the small region on the disc. But as the disc rotates and when this region is close to the iron core electromagnet, the number of field lines passing through the region increases. Magnetic flux is essentially just a measure of the number of field lines passing through perpendicular to something and magnetic flux density is like the number of field lines passing through something perpendicular to it per unit area.


Lenz's law states that the induced emf acts in a direction such as to oppose the magnetic flux change that caused it. However Fleming's right hand GRIP rule can tell you the CONVENTIONAL (+-->-) current direction if you already know the magnetic field direction (N-->S). Alternatively it can tell you the magnetic field direction if you already know the current direction.

The initial position of the small region in the disc I was talking about is the pink dot on the disc there (left). The final position of the same small region in the disc after some rotation is the red dot on the disc (under the iron core). See

http://macao.communications.museum/images/exhibits/2_2_4_2_eng.png

So at the red dot, just under the iron core, there's high magnetic flux through it, but at the pink dot there's little magnetic flux through it. Thus as the region moves from pink to red, Theresa magnetic flux change.

But your also saying that magnetic flux is changing too,

magnetic flux = Φ. And magnetic flux linkage = Δ(NΦ)

So if Φ is changing, surely the flux linkage is too? So by faradays law, an emf is induced in this way?

Where am i going wrong?

I dont quite understand, is the region supposed to be where the flux lines cut through the disc? If so, how did you work that out? Doesnt the field lines cut through anywhere on the disc? As you can probably tell, i'm very lost...

The region is just a general region I chose on the disc to illustrate my point of changing magnetic flux.

Also, magnetic flux linkage I tend to use when talking about a coil of wire of the magnetic flux linking it.

Thanks for clearing that up. Ill try and be careful when using such key terms in questions. (Those links are very helpful!)