Induction (1 Viewer)

[kimmeh]

When an aluminium disk os dropped between the poles of a stack of powerful horseshoe magnets, it "floats" down. Explain the effect

eddy currents are induced in the aluminium plate. theres something else i have to explain. just not quite sure what it is..

 

[wogboy]

The reason the aluminium disk falls down slowly is because of eddy currents being induced in it. Because of Lenz's law these eddy currents cause an opposing magnetic field to occur. The interaction of this opposing magentic field with the original magnetic field causes a force to act on the aluminium disk opposing the direction of motion. This force (which is upwards in this case) slows the disk as it falls.

Analogy: The "opposing force" is proportional to the velocity at which the disk falls, so this is similar to dropping a feather in air. The feather falls due to gravity, but air resistance provides an opposing force slowing it down.

 

[+:: $i[Q]u3 ::+]

nice analogy =)
the same thing happens when you get a metal tube and drop a bar magnet down it -
remember, whenever you have a current, you have a magnetic field.
eddy currents generate their own magnetic fields. The direction of hte magnetic fields will always be such taht it opposes the initial change in magnetic flux.
So the eddy currents' magnetic fields will interact with the horseshoe magnet fields and result in a force upwards. i.e. force due to gravity is reduced, and the disc falls with slower acceleration.

 

[Rahul]

the currents induced will infact create a magnetic force, that will oppose the motion. this is lenz's law. so not only will the gravitational force be pulling it down, but due to lenz's law [which will oppose the motion] will be pushin it up.

it WONT be because the magnetic field will interact with the metal, aluminuim, because that will have no effect. try taking a magnet near an aluminium can.