Magnetic force does no work. OR does it?

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Discussion Overview

The discussion centers around the concept of magnetic force and its relationship to work done on charged particles, particularly in the context of a U-shaped wire loop with a movable metal bar in a magnetic field. Participants explore whether the magnetic force does work on charges and how induced electromotive force (emf) relates to this concept.

Discussion Character

  • Debate/contested

Main Points Raised

  • Some participants assert that the magnetic force does no work on moving charged particles, as it does not change their kinetic energy but only alters their trajectory.
  • Others propose that in the scenario of a movable metal bar in a magnetic field, the induced emf suggests that the magnetic force is responsible for setting charges into motion, raising questions about whether this constitutes work being done.
  • A participant suggests that the magnetic field may be acting as a medium that transfers kinetic energy from the moving bar to the charges, rather than doing work directly.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the magnetic force does work. There are competing views regarding the nature of energy transfer and the role of the magnetic field in this process.

Contextual Notes

The discussion highlights the complexity of defining work in the context of magnetic forces and the assumptions involved in interpreting energy transfer between the moving bar and the charges.

fisico30
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Hello Forum,

it is well known that the magnetic force |F_mag|= q v B sin(theta) does no work on a moving charge particles, i.e. it does not increase or decrease its kinetic energy. It only changes its trajectory.

However, in the examples of a U shaped wire loop with a movable metal bar that is free to slide, if we move the bar with velocity v while the loop is inside a magnetic field B, an induced emf= vBL is generated. It is said that the induced current (charges in motion) is due to the magnetic force...that seems an inconsistency: the charges are now set into motion by F_mag...So F_mag does work on them...or doesn't?

thanks,
fisico30
 
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The metal bar will slow down, the magnetic field is simply transferring the kinetic energy of the moving bar into the kinetic energy of the charges.
 
Hi Matterwave

so your point is that the magnetic force is not actually doing the work...it is just transferring it? Is the magnetic field kind of acting as a proxy you mean?
 
Sort of I guess. It's just transferring one kinetic energy into another.
 

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