Can Fleming's Right Hand Rule Be Used When Magnet Moves Parallel to Coil?

AI Thread Summary
Fleming's right hand rule can be applied to determine the direction of current when a magnet moves into a coil, even if the magnetic field and movement appear parallel. The discussion clarifies that the magnetic field is directed from north to south, and the movement of the magnet can create a varying magnetic field in the coil. Using the right hand generator rule, one can analyze the induced electromotive force (emf) by considering the movement of the solenoid relative to the stationary magnet. Lenz's law further explains that the induced current will flow in a direction that opposes the change in magnetic flux, resulting in an anticlockwise current when viewed from above. Understanding these principles helps clarify the confusion regarding the application of the rules in different scenarios.
GeneralOJB
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Can I use Fleming's right hand rule to determine the direction of current when a magnet is moved into a coil(s) of wire? I am finding it difficult because the magnetic field and movement are parallel instead of at right angles.

If not, does this mean I am only allowed to use it when a wire moves in a magnetic field (at right angles)?
 
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Are you sure they are parallel? I don't think so.
 
dauto said:
Are you sure they are parallel? I don't think so.

This is what is confusing me then.

Consider a set-up like this:
Coil_07.JPG


The magnet field points up (north to south) and the movement is also vertical, so the field and movement are parallel.
 
GeneralOJB said:
Coil_07.JPG


The magnet field points up (north to south) and the movement is also vertical, so the field and movement are parallel.
Where is the south? Down? Magnetic field is from North to south.
 
adjacent said:
Where is the south? Down? Magnetic field is from North to south.

The south is on the other end of the magnet, above the north.
 
GeneralOJB said:
The south is on the other end of the magnet, above the north.
bar-magnet-magnetic-field.jpe

Is the field parallel to the bar?
 
adjacent said:
bar-magnet-magnetic-field.jpe

Is the field parallel to the bar?

Yes (I presume so).
 
attachment.php?attachmentid=70417&stc=1&d=1402160128.jpg

Do you see why it's not parallel now?
 

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adjacent said:
attachment.php?attachmentid=70417&stc=1&d=1402160128.jpg

Do you see why it's not parallel now?

I was told that the field is from north to south, so is that not really true then? It seems the field is both perpendicular and parallel from that diagram. Also how can I use the left hand rule to determine the direction of current in this case if the field is going in infinitely many different directions perpendicular to the movement?
 
  • #10
GeneralOJB said:
how can I use the left hand rule to determine the direction of current in this case ?
I wanted an answer to this problem too but I didn't really understand what my teacher told me.

The problems with infinite field lines seems far too advanced to me. May a more experienced member help thou and myself.
dauto!
 
  • #11
(1) It's the right hand generator rule that you need. (2) Suppose the magnet to be stationary and the solenoid moving up the page in the diagram in post 8. (3) Now concentrate on just one small section of wire in the solenoid; let's choose the piece in the top front of the coil. (4) Observe that in the region of this section of wire the magnet's magnetic field is more or less coming out of the page towards you. (5) So point first finger of right hand out of the page and thumb up the page (the way the wire is moving. (6) Then your second finger will point in the direction of the induced emf. You should find that this is roughly from left to right - if you haven't dislocated any joints. (7) You'll find the same result: emf anticlockwise (looking from above) around the solenoid whichever section of wire you choose.

There's a much nicer way of finding the direction of the induced emf in cases like this: use Lenz's law… The current that will flow as a result of the emf if we short-circuit the coil (join its ends together) will produce a magnetic field which will oppose the coming together of the magnet and the solenoid. So the top end of the solenoid will become a North pole, that is flux lines will come upwards out of it. Using the right hand grip rule, we can deduce that the current, and hence the emf, in the coil is anticlockwise (seen from above).

It would be nice if you say whether this is of any help...
 
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