We Can Figure This Out.org
Virtual Lab: Scanning Electron Microscope (SEM)
University of Virginia
             
 
© 2003-Present, John C. Bean
 
Here we have made the magnetic field visible. It moves in loops down through the core of the lens (its? direction is indicated by the yellow markers).

As the magnetic field is increased (by passing more current through the electro-magnet), the field expands and has the effect of moving the electrons more tightly together.

 
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