Magnetic force does no work. OR does it?

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SUMMARY

The discussion centers on the concept that magnetic force, defined by the equation |F_mag|= q v B sin(theta), does not perform work on moving charged particles, as it does not alter their kinetic energy but only changes their trajectory. A scenario involving a U-shaped wire loop with a movable metal bar illustrates this principle, where moving the bar within a magnetic field B induces an electromotive force (emf) of vBL, leading to induced current. Participants clarify that while the magnetic force influences the motion of charges, it merely transfers kinetic energy from the bar to the charges, rather than doing work itself.

PREREQUISITES
  • Understanding of electromagnetic theory, specifically Lorentz force.
  • Familiarity with Faraday's law of electromagnetic induction.
  • Knowledge of the concepts of kinetic energy and energy transfer.
  • Basic grasp of electric circuits and induced current.
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  • Study Faraday's law of electromagnetic induction in detail.
  • Explore the relationship between magnetic fields and induced currents.
  • Investigate the concept of energy transfer in electromagnetic systems.
  • Learn about the implications of the Lorentz force in various physical scenarios.
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Physics students, electrical engineers, and anyone interested in the principles of electromagnetism and energy transfer in magnetic fields.

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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