argh eddy currents... please explain (1 Viewer)

[Aerials]

could someone PLEASE explain eddy currents to me in simple terms... I just dont seem to understand what the hell is going on there. I would appreciate it heaps! Thanks in advance

 

[Affinity]

If a piece of metal is placed in a changing magnetic field, there will be electric currents flowing through it(eddy currents). Since the piece of metal would have close to no resistance, the currents would be quite high.

I am afraid this is oversimplified though.. search the board for previous threads

 

[lana_liana]

Eddy currents obey Lenz's Law and therefore are induced in a direction so as to oppose the change that created them.

For example:
A spinning metal wheel (conductor) induces eddy currents because of it is spinning. Via Lenz's Law, these eddy currents will oppose this change and then stop the wheel from spinning (smoothly), which is then electromagnetic braking.

 

[Xayma]

It smoothly stops because the force the eddy currents provide would be directly proportional to its to speed. Hence it will start slowing down slower near the end which results in a smooth stop.

 

[t-i-m-m-y]

the posts above do not seem to explain eddy currents

timmys tutoring version:

first of all we have changing magnetic fields. these changing magnetic fields induce some sort of changing electric field/current. (remember electromagnetic induction; like space/time intracacies, so is magnetism and electricity connected)
*cough anywayz. these changing electric currents induced, when in metals are called eddy currents. they are circular.

so now we move to lenz's law. at its basis, it dictates which way the eddy currents will flow. there should be another dot point on the relationship between len'z law and conservation of energy. but basically the others have said above, the polarity of the eddy currents will be such to oppose the change that caused em.

this is because if they did not oppose the change that caused em, the associated magnetic fields with the eddy currents would "reinforce" the original magnetic field, which would produce/induce even bigger eddy currents, leading to a infinite eddy current... which we know is impossible

hope that helps
*goes back to uni chemistry and shrodinger's equation, *rubs hands in evil glee

 

[cko]

basically all u need to know is:
when a metal is placed in a magnetic field then it will produce a current right? Like electrical wires. Well if u put a big block or sheet of metal in that magnetic field then u will also get a current. These currents in the sheet of metal will moce around ina circular firection because there is so much space. These circular moving currents are what u call eddy currents. it's just moving electrons in a sheet of metal and not in a wire.

 

[t-i-m-m-y]

Originally posted by cko
when a metal is placed in a magnetic field then it will produce a current right?

a changing magnetic field. should i add

 

[xiao1985]

Originally posted by t-i-m-m-y
a changing magnetic field. should i add

or... a relative motion between the conductor and the magnetic field...

 

[Xayma]

Originally posted by xiao1985
or... a relative motion between the conductor and the magnetic field...

Fine a change in magnetic flux in the conductor.

 

[t-i-m-m-y]

Originally posted by Xayma
Fine a change in magnetic flux in the conductor.

or d(phi)/dt must exist

ie. there must be a change in magnetic flux over a change in time