No Electromagnetic Force in Moving Magnet & Solenoid

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Discussion Overview

The discussion revolves around the electromagnetic forces experienced by a solenoid when a magnet is moved towards it. Participants explore the existence of Laplace (Lorentz) force in relation to induced currents and magnetic fields, questioning the conditions under which these forces manifest. The conversation includes theoretical considerations, practical implications, and specific scenarios involving circuits and magnetic fields.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • Some participants assert that while a voltage difference is induced in the solenoid, there is no Laplace force acting on it, questioning the conditions under which such a force would exist.
  • Others argue that there is indeed a Laplace force on the windings of the solenoid, suggesting that the forces on different parts of the coil may cancel each other out, resulting in no net force.
  • One participant proposes that the induced current creates a reaction force in the direction of the approaching magnet, implying a repulsive interaction.
  • There is a discussion about whether the electromagnetic forces acting on the solenoid can be considered a net summation of forces, with some suggesting that torque may also play a role.
  • Participants explore the relationship between induced electromotive force (emf), current, and force, questioning the accuracy of statements regarding their interdependence.
  • Questions arise about the existence of Laplace force on all components of a circuit, not just the sliding conductor, with some asserting that it applies to any wire carrying current in a magnetic field.
  • Clarifications are sought regarding the implications of Maxwell's equations and the geometry of the circuit in determining current and force.
  • Some participants express confusion about the distinction between providing a wire and providing current, indicating a need for further clarification on these concepts.

Areas of Agreement / Disagreement

Participants express differing views on the existence and implications of Laplace force in the context of the solenoid and moving magnet. There is no consensus on whether the forces cancel out or if a net force exists, and the discussion remains unresolved regarding the relationship between induced emf, current, and force.

Contextual Notes

Participants reference various scenarios involving circuits, magnetic fields, and the application of Maxwell's equations, highlighting the complexity of the relationships involved. The discussion includes assumptions about the geometry of the setup and the behavior of the components under different conditions.

  • #31
brainyman89 said:
if we have a solenoid suspended freely and no current is traversing it, and we approach a magnet toward it, would it repel or rotate?
That is a good question, I guess it would depend on the exact geometry, but I don't know for sure.

brainyman89 said:
can we consider a solenoid totally as a bar magnet when a current traverses it??
The magnetic field of a solenoid is very similar in shape to the magnetic field of a bar magnet, but I don't know what you mean by "totally".

brainyman89 said:
my another question is: when we are providing a wire, u r considering that we are providing current, this is confusing me there is a wide difference between a wire and a current?
Yes, there is a wide difference between a wire and a current. However, in all of your examples so far you have a changing flux in a circuit and therefore an emf and therefore a current in the wire. If you made a different example then I would answer differently, but so far you have only made examples of wires with currents.
 
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  • #32
You provided B and a means of determining I (wire/resistor geometry and composition) using Maxwell's equations. From B and I you obtain f. You provided both B and I, although the I is hidden:

Did u mean in this statement that providing variable B equals providing B and I (i.e variation=current), hence i will get B and I thus producing F.
 
  • #33
brainyman89 said:
Did u mean in this statement that providing variable B equals providing B and I (i.e variation=current), hence i will get B and I thus producing F.
Essentially, but I would have said "providing variable B and wire/resistor geometry equals providing B and I".
 

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