A magnetic field deflects an electron beam, but work on the beam

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A magnetic field can deflect an electron beam without doing work on it because the magnetic force acts perpendicular to the electron's velocity. This perpendicular force changes the direction of the beam but does not alter its kinetic energy. Since work is defined as a force causing displacement in its direction, no work is done in this scenario. The kinetic energy of the electrons remains constant despite the change in direction. Understanding this principle is crucial in the study of electromagnetism.
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A magnetic field deflects an electron beam, but it can not do any work on the beam. Why? :confused:
 
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It does not change the kinetic energy, only the direction.

The gotcha is that kinetic energy is frame dependent, but this feature is probably not of primary interest to you at this point.
 
Another way of saying what turin just said is that the magnetic force is always perpendicular to the electron's velocity: No work is done since there is no displacement in the direction of the force.
 
thank you for the help. :)
 
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So here is the motional EMF formula. Now I understand the standard Faraday paradox that an axis symmetric field source (like a speaker motor ring magnet) has a magnetic field that is frame invariant under rotation around axis of symmetry. The field is static whether you rotate the magnet or not. So far so good. What puzzles me is this , there is a term average magnetic flux or "azimuthal mean" , this term describes the average magnetic field through the area swept by the rotating Faraday...
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