Doubts About Extending - Fleming's Right Hand Rule

Have no idea what you're on about.....

http://www.magnet.fsu.edu/education/tutorials/java/handrules/

I have a hard time remembering which rule to use, but if your shield is in motion, and if it interacts with the magnetic flux lines, there will be a current conducted in the shield. The type of metal used as a shield will make all the difference. Even aluminum will interact with the magnetic flux lines. Aluminum is used in transformers to save money when the copper prices are so high.

In general, your "X axis" conductor will be subject to induction if it is in motion relative to the magnetic flux lines. And, since flux lines bend, it just might be impossible to give an intelligent answer to your question without more information. It is really a 3D problem, and unfortunately, the picture is only 2D.

The illustration you provided may be causing some of your confusion.

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Lines of magnetic flux are often better represented by complete paths, instead of rays in a particular direction. Similarly, if you are going to discuss electrical current, a better representation of a circuit is a complete path and not a ray in a particular direction.

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With those things in mind draw a new illustration. The topology of the two loops (electrical and magnetic) dictates the possible results of introducing shielding. It may be more helpful to think of the shielding 'rerouting' the flux, rather than 'cutting' it since the flux will remain as a complete path, only over a new route when the shielding is introduced.

I use the Budweiser right hand rule.

If it works when I plug it in, that's good.

If it doesn't work, I call the man and have a Bud.

_{(Note to self: EE's have no sense of humor)}

Your illustration looks like a linear motor where current in the rail interacts with alternating magnetic fields.

Current is never "generated". Only Voltage or EMF can be generated. In a closed circuit, this voltage will "cause" a current to flow. Fleming's Hand Rules only mention "Direction of Current Flow in the conductor" and NOT "CURRENT GENERATED". Please re-read the rules more carefully.

It would be pretty easy to establish that in any real system, current is always generated.

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The conductor in a real system would be of some non negligible length and would also have some minimal amount of capacitance. Since the effect is based on the net displacement of electrons, whether you prefer looking at segregation of charge by displacing the electrons, or you are looking at flow of electrons, those things both rely on transport of electrons.... which is pretty much current.

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Besides, if it was only a buildup of voltage, then you wouldn't need a conductive path....winding a dielectric would work perhaps even better.....but in reality you do need a current path because the buildup of any voltage is realized by the flow of electrons.

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There are legitimate explanations from either perspective. The important thing to remember is that "all models are wrong, some are useful" voltage and current are just two components of a man made model that happens to work really well. So well, that some people get mixed up and think that it actually describes what is going on, instead of merely allowing accurate prediction of outcome.

As you conductor moves as is shown in the upper diagram, a voltage is induced as it cuts the magnetic field lines.

A magnetic shield does not block magnetic field lines, it reroutes them. In the diagram shown, the field would be concentrated not in the slots but in the ferrous material between the slots. Now if this slotted structure moved perpendicular to the wire, it would work like a generator with permanent magnets on the rotor and generate an AC voltage in the wire (or the stator).

If I understand your diagram, you have interposed a slotted shield between a conductor and a magnetic field. The effective magnetic flux is then reduced, being determined only by the proportional areas of the slot and the shield material. The fact that the shield is moving means nothing unless that proportion varies.

I am re-writing the diagram. Some have said voltage will be generated and current will flow in the direction etc etc. Take it that voltage is generated and when the current path is closed- current passes in the direction shown (all as per Fleming's right hand rule.

Kindly focus on the problem posed - where we are not moving the magnetic field or the conductor - but only a magnetic shield - to cause variation in the magnetic field - will there be induced voltage and hence current flow - I doubt and do not expect nay induced voltage.

Let us accept that Fleming's right hand generator rule works and there is no doubt about it. It states that when a copper conductor is moved in a permanent magnetic field, current is generated in the conductor - as per Fig 1 below.

Now take the case of a transformer where the magnetic field is varying and there is no mechanical movement of the conductor. Yet current is generated due to varying magnetic flux. This is also observed and proven as we have working transformers.

Now let us come to what I am looking for where we have a permanent magnetic filed and a static conductor. The magnetic field is mechanically chopped by a slotted magnetic shield as in Fig 3 or 4. Question is - will nay current be generated in the conductor- my hunch is NO. Has any one conducted any experiment to prove to the contrary?

Part of your premise is wrong: the effect of a magnetic shield will be to move the lines of flux, it does not function as if you were reducing current on an electromagnet. The lines of magnetic flux are continuous loops.

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If there were a shield that simply negated the field then an analogous situation would be an explosively pumped ferromagnetic pulse generator. These devices consist of usually a single turn of copper around a ring (cylinder with small diameter axi-symetric hole) neodymium magnet (axis aligned). The center is filled with explosive and a detonator and a cushion is put between the outside of the magnet and the single turn.

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When the pulse is needed, the explosive is initiated. The pressure wave destroys the magnet very rapidly, this creates an enormous surge in current.

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If you had shielding material that somehow reduced the flux rapidly it would probably behave in a similar way. But I don't know of any shield that does anything other than reroute the path.

In figure 4 you will get an alternating voltage, but not for the reason that you think.

As others have pointed out, a magnetic "shield" does not block the magnetic lines of force. A magnetic "shield" merely provides a low "resistance" path for the magnetic lines of force. In other words, the magnetism would much rather flow through iron than air. In figure 4, the magnetic lines of force will be concentrated through the iron pieces. As the belt moves, the lines of force will alternate from one side of the wire to the other and back again, generating an alternating voltage. In figure 3, nothing will happen.

"Now take the case of a transformer where the magnetic field is varying and there is no mechanical movement of the conductor. Yet current is generated due to varying magnetic flux. This is also observed and proven as we have working transformers."

Perhaps you can explain how a "transformer" "generates" electricity.

I will be out of station over next few eeks and may not be able to respond.

As far as transformer is concerned V = -N dø/ dt works. Hence flux is varying by itself. Voltage is induced as flux varies. Now we are talking of permanent magnetic flux and not varying flux. Further the conductor is also static. As per Fleming's rule - mechanical movement is essential- while in the extension of Fleming's rule- I am trying to keep both the magnet and the conductor static. Attempt is to vary flux - how? That is the crux of the problem.

I am not using ferrite to cause this change. Ferrite is to complete the magnetic path and copper is used to complete electrical path. I am trying to see interaction between magnetic path and electrical path- without involving mechanical motion.

This appeared below "The way to get started is to quit talking and begin doing." -- Walt Disney-

So I believe in physically condcuting experiements as far as this topic is concerned.

You are putting energy into a transformer, and not getting additional energy out.

Indeed, you are losing energy in a transformer, not generating it.

Without motion, you cannot "generate" power.

Please correct me if I'm wrong.

'...Without motion, you cannot "generate" power....'

Technologies using thermoelectrics, photovoltaics, and chemical batteries suggest you implied (or intended to imply) restrictions on your assertion that I am missing.

You are right.

I was referring to the classical, mechanical means of generation.

I stand by my position that transformers do not "make" electricity.

I agree with you about transformers not making electricity.

It would also be very difficult for me to disagree with the idea that a mechanical means of generation would necessarily involve motion.

So what exactly are you using for your shield material? And how are you going to create a time varying flux without movement?

I keep reading / following every comment. try to analyze and actauly conduct experiments to verify claims. I have a DSO, Ferrite and Neodymium magnets, as well as soft ferrite blocks etc etc- a full fledged lab for this project. So far I have not seen any build up of voltage in the condcutor.

Sounds like it is time to reevaluate this experiment with the topology dictated possibilities of the critical loops, namely the magnetic flux lines and the electrical path.

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So, if you are using ferrite as your 'shield', you may not be getting a lot of shielding. Laminated electrical steel that provides an alternate return path not through your conductors would probably be better.

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How many windings do you have passing through?

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Just as a quick verification, without the ferrite, take one of your magnets and wave if past your conductor in your set up and make sure that you are seeing some indications of voltage change.

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Perhaps you could take pictures of your experimental setup thus far and post for us to see?"

I wouldn't expect much. It should only be momentary as the ferrous block moves past the wire. The quicker it moves, the greater the voltage. The gap should be bigger than the blocks and the wire should be as close as possible.

Look at it this way: The ferrous pieces in your belt become magnets in the magnetic field. (A nail close to a magnet will pick up small pieces of iron.) If you move a magnet across a wire (figure 4) you induce a small voltage. Moving it along the wire (figure 3) will not induce a voltage.