Magnetic force does no work. OR does it?

[fisico30]

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

 

[Matterwave]

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.

 

[fisico30]

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?

 

[Matterwave]

Sort of I guess. It's just transferring one kinetic energy into another.