Motoring Effect in DC Motors: Magnetic Field Interaction or Lorentz Force?

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Discussion Overview

The discussion centers on the motoring effect in DC motors, specifically exploring the mechanisms that produce torque when current flows through the armature winding. Participants debate whether the torque arises from the interaction of magnetic fields or the Lorentz force acting on the electrons in the conductor. The conversation includes theoretical considerations and technical explanations related to magnetic fields and forces in the context of motor operation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that torque is produced due to the interaction of magnetic fields created by the armature and field currents.
  • Others argue that the torque results from the Lorentz force acting on the electrons in the conductor, questioning the nature of the force and its origin.
  • A participant mentions that the magnetic field has an energy density and that nature seeks to minimize this energy by rotating the motor.
  • There is a discussion about whether two magnetic fields can interact, with some asserting that they cannot overlap or interact, referencing Ampere's law.
  • One participant raises a question about the back electromotive force (emf) and its relation to the hidden wires in the motor slots.
  • Another participant discusses the effects of a wire carrying current placed in a magnetic field, suggesting that it distorts the original flux and could lead to a resultant force.
  • Quantum physics is briefly mentioned, with a suggestion to explore virtual photons and their role in electric forces, though this leads to further complexities.
  • There is a reference to the cross product mechanism in determining the direction of force, with a suggestion that magnetic fields do not interact in a conventional sense.
  • Participants express uncertainty about the nature of the forces at play, questioning whether the force is due to the distorted magnetic field or the motion of charges in the magnetic field.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the motoring effect is primarily due to magnetic field interaction or the Lorentz force. Multiple competing views remain, with ongoing debate about the nature of forces in DC motors.

Contextual Notes

Some claims rely on specific definitions of magnetic fields and forces, and there are unresolved questions regarding the interaction of fields and the conditions under which forces are generated. The discussion also touches on complex concepts such as armature reaction and back emf, which may not be fully explored.

  • #31
cnh1995 said:
Seems that it's not as straightforward as it looks in the diagram.. Thank you very mucha for your patient replies.. I hope I didn't bore you with this long thread..

not at all, i wondered what you were driving at.

There's always several ways to teach a subject.
My vector calculus is rusty .
Somebody who's fluent in it might prefer that approach.
old jim
 
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  • #32
jim hardy said:
not at all, i wondered what you were driving at.

There's always several ways to teach a subject.
My vector calculus is rusty .
Somebody who's fluent in it might prefer that approach.
old jim
Just one last question..If I placed another wire very close to the original wire in the diagram and sent current through it in the opposite direction, the resultant magnetic field due to both the currents will be almost 0. Will there be a force on the wire?? There won't be any distortion of flux as seen in the original diagram. Will Lorentz force act on them??
 
  • #33
Not trying to duck your question here...

I assume your two wires are physically kept close together by something like glue , or their innate rigidity ? If not the geometry will change and the problem becomes dynamic.

I'll answer that each wire will experience a vertical force from its Lorentz force effect and those forces of course sum to zero. (ignore the torque couple for now)

and there's an additional force on each wire from the other one
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/wirfor.html
of course you postulated current in opposite directions not same direction as in this figure - so wouldn't that force be repel not attract ?
wirefor.gif

I've been thinking nights about your questions

and they make me ponder what is nature of space that force is transmitted between objects over a distance by magnetic and electric and gravity fields?
Higher math is able to describe the interactions out there in free space not just at the objects.

But we can only sense the resulting force at an object like a wire or a charged piece of matter where we can attach a force measuring device..
I need an aether.

I think that's why i stick with my 19th century analogies - my algebra is so prone to mistakes that i have to visualize the forces before i'll believe the math.
That is a handicap. I really advise you to master Vector Calculus and Maxwell's equations, they've become the coin of the realm.

old jim
 
  • #34
ps thanks for your patience with me .
 
  • #35
jim hardy said:
ps thanks for your patience with me .
Thanks a lot..:-)I think its time for me to start working on higher math..
 
  • #36
cnh1995 said:
I think its time for me to start working on higher math..
There are plenty of extraordinarily capable people here at PF ...

I'll not pretend I'm qualified to teach vector calculus.

Still learning something every day --

old jim
 

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