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Externet

Current generation by moving magnet...

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Hello all.

If a magnet is spun, moved, shaken while surrounded by a coil, the coil will generate a voltage that would flow as current if the coil has a closed circuit.

If a magnet is moved inside mercury, the currents would be 'tridimensional',  in the body of the conductive liquid, probably emphasized in a plane/direction depending on the plane of the magnet motion.  Do I have it right to this point ?

If the magnet moving inside the conductive mercury is a conductor itself, and in intimate contact with the currents flowing in the mercury, will the current share paths in and out of the fluid ?

If the magnet moving in conductive fluid is covered with an insulating paint/coat of glass, rubber, whatever; will the electric currents be confined only to the fluid ?

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Trying with different wording...

Are eddy currents also generated in a conductive fluid when a magnet is moved submerged in it ?     The eddy currents going in circles, do they create magnetic fields of their own, as if they were currents in loops of wire ?

Reversed :  a stationary magnet inside a pipe where mercury flows.  Is there generation of eddy currents in the conductive fluid ?

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20 hours ago, Externet said:

 

If the magnet moving inside the conductive mercury is a conductor itself, and in intimate contact with the currents flowing in the mercury, will the current share paths in and out of the fluid ?

 

I would expect so. I must admit I have difficulties imagining how exactly would a 'swirl' of the current look around the magnet moving through mercury. A computer simulation might come good.

20 hours ago, Externet said:

 

If the magnet moving in conductive fluid is covered with an insulating paint/coat of glass, rubber, whatever; will the electric currents be confined only to the fluid ?

 

Of course.

1 hour ago, Externet said:

Are eddy currents also generated in a conductive fluid when a magnet is moved submerged in it ?     The eddy currents going in circles, do they create magnetic fields of their own, as if they were currents in loops of wire ?

Of course. all currents, including eddy currents, generate magnetic field.... That is, when computing total magnetic field, you will have to include contribution from eddy currents.

1 hour ago, Externet said:

Reversed :  a stationary magnet inside a pipe where mercury flows.  Is there generation of eddy currents in the conductive fluid ?

Yes (in classical electrodynamics these are from different principle, but the effect is the same)

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Current at any point is in one direction, not tridimensional.

 

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Posted (edited)
4 hours ago, Danijel Gorupec said:
On 6/3/2020 at 10:15 PM, Externet said:

 

If the magnet moving in conductive fluid is covered with an insulating paint/coat of glass, rubber, whatever; will the electric currents be confined only to the fluid ?

 

Of course.

Thanks.  I have a problem with this :  The metallic and electrically conductive magnet insulated by rubber from the mercury is exposed to the proximity of the eddy currents in the mercury which are generating their eddy magnetic fields.    Being the magnet in motion, would such eddy magnetic fields induce electrical currents back into the conductive metallic moving magnet body ?

Seems some reciprocal interaction can happen...  Am aware I used/described the words "eddy magnetic field"  😳  which have never seen before; only "eddy electrical current"

Edited by Externet

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3 hours ago, Externet said:

Thanks.  I have a problem with this :  The metallic and electrically conductive magnet insulated by rubber from the mercury is exposed to the proximity of the eddy currents in the mercury which are generating their eddy magnetic fields.    Being the magnet in motion, would such eddy magnetic fields induce electrical currents back into the conductive metallic moving magnet body ?

Seems some reciprocal interaction can happen...  Am aware I used/described the words "eddy magnetic field"  😳  which have never seen before; only "eddy electrical current"

Good point! I didn't think about it. You might be well right... As with the first point, I cannot tell for sure without some numerical computation. But I guess you are most likely right.

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15 hours ago, swansont said:

Current at any point is in one direction, not tridimensional.

Thank you, sir.

Can current exist when referred to a point ?  Can direction exist when referred to a point ?  Should current and direction be referred instead to a line/location/flow between two points ?

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42 minutes ago, Externet said:

Thank you, sir.

Can current exist when referred to a point ?  Can direction exist when referred to a point ?  Should current and direction be referred instead to a line/location/flow between two points ?

Current will have a value and direction at all points that the current exists. A line would not work, since current can follow e.g. circular paths.

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16 hours ago, Externet said:

Can current exist when referred to a point ?  Can direction exist when referred to a point ?  Should current and direction be referred instead to a line/location/flow between two points ?

Do I assume correctly that you are talking about current intensity, not current density (when you just say 'current', I am not sure)?

Current intensity is not defined for a point (also not for a line between two points). Current intensity, as it is mostly understood, is referred to a surface - it is a flow of charge through a surface in a unit of time. Basically, when you talk about current you should also mention (or assume) the surface through which this current flows to make its value meaningful.

Generally, direction does make sense when referred to a point (vector values are often like that). However the value of current intensity is usually not understood as a vector value - it is taken as a scalar.

15 hours ago, swansont said:

Current will have a value and direction at all points that the current exists.

So, this would be correct for current density, but not for current intensity (I am not sure which one Swansont actually meant, but I assume the question was about current intensity) The current intensity is an integral value and so does not have a finite value for a point and does not have a direction.

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4 hours ago, Danijel Gorupec said:

So, this would be correct for current density, but not for current intensity (I am not sure which one Swansont actually meant, but I assume the question was about current intensity) The current intensity is an integral value and so does not have a finite value for a point and does not have a direction.

If you’re not assuming an idealized system. But quite often we assume the current is in, e.g a one-dimensional line. Such as when discussing the field around a current-carrying wire. The wire is not given a radial extent.

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Indeed. As an electrical engineer, I imagined current intensity to be vector-like my whole life - a thing that runs through one-dimensional wires. So I reacted with disbelief when first read that generally the current intensity is considered a scalar. It took me some time of more careful thinking to accept this fact.

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