Quizzes & Puzzles3 mins ago
Induced current
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If an iron ball was to pass through a tight coil of wire to produce an electric current, would this cause the ball to slow down at all? What I mean is, if a toaster or something was wired up to the ball/coil then an energy transfer would take place to heat the toast. Does the energy come from slowing down the ball? I asked our physics teacher and he says 'No' and he really knows what he's talking about, which leaves me in confusion. For example, if a really big coil was suspended in space around the Earth, in the shape of a ring, and the ball was orbiting inside it, you surely couldn't run electrical devices off it forever, could you?
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If the iron ball manages to induce a current in the coil then yes, the ball would slow down.
I think your question about where the energy comes from is badly phrased - the slowing ball doesn't provide the energy. The energy comes from a magnetic flux cutting a conductor, the prime mover (in this case the movement of the ball) provides the power, the flux cutting provides the method of power conversion, in your example, movement into electrical energy. If 'work is done' then the ball's movement must change, ie slow down.
I think that your physics teacher is correct but is answering you generally - you would find that the movement of an iron ball past a coil would be unlikely to induce current into the coil, it may induce an e.m.f. from its remnant magnetism, but would not have sufficient flux density to generate (in)significant power.
Finally, a ball orbiting inside a large coil isn't going to cut the conductor with its flux, your motion is wrong, so you will not generate here either. Even if your motion was correct, power used would slow the ball and it would lose its orbit and fall back to earth.
Type flux induced emf into Google and you will find a bunch of useful topics on Faraday's and Lenz's laws.
(http://physics.bu.edu/~duffy/PY106/InducedEMF.html was quite readable)
I think your question about where the energy comes from is badly phrased - the slowing ball doesn't provide the energy. The energy comes from a magnetic flux cutting a conductor, the prime mover (in this case the movement of the ball) provides the power, the flux cutting provides the method of power conversion, in your example, movement into electrical energy. If 'work is done' then the ball's movement must change, ie slow down.
I think that your physics teacher is correct but is answering you generally - you would find that the movement of an iron ball past a coil would be unlikely to induce current into the coil, it may induce an e.m.f. from its remnant magnetism, but would not have sufficient flux density to generate (in)significant power.
Finally, a ball orbiting inside a large coil isn't going to cut the conductor with its flux, your motion is wrong, so you will not generate here either. Even if your motion was correct, power used would slow the ball and it would lose its orbit and fall back to earth.
Type flux induced emf into Google and you will find a bunch of useful topics on Faraday's and Lenz's laws.
(http://physics.bu.edu/~duffy/PY106/InducedEMF.html was quite readable)
I ask this because the same person showed us a demonstration of induced current with a metal rod and a whole load of coils. He poked the rod in and out of the coils (to stifled laughs) and this made a bulb flicker. To extend the question, would twice as many coils slow down the object twice as much, provided it cuts the field and all that? Does the resistance of the wire make any difference, and would it be possible to set up a tube of coils so dense that, if you dropped some iron down it, it would only fall really, really slowly? Thanks to tomr for above answer, by the way.
If the rod was magnetised this would indeed induce current and make the lamp flicker.
Yes, twice as many turns would increase the effect, the flux would cut two conductors and induce the same current in each, the fact that they are different parts of the same conductor is irrelevent, the result would be the sum of the two inductions.
The slow falling effect can be achieved by dropping a magnet with a dense field down an aluminium tube.
The eddy currents (induced currents) in the aluminium take sufficient energy from the movement of the magnet such that it creates 'friction'. Would it stop? No, because it has to move in order for the currents to be induced so an equilibrium will be achieved.
Yes, twice as many turns would increase the effect, the flux would cut two conductors and induce the same current in each, the fact that they are different parts of the same conductor is irrelevent, the result would be the sum of the two inductions.
The slow falling effect can be achieved by dropping a magnet with a dense field down an aluminium tube.
The eddy currents (induced currents) in the aluminium take sufficient energy from the movement of the magnet such that it creates 'friction'. Would it stop? No, because it has to move in order for the currents to be induced so an equilibrium will be achieved.
here is a site on how to do the 'slow fall' experiment with a magnet and a copper pipe: http://madlabs.info/index.php?x=slomo_mag.jsp
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