https://www.youtube.com/watch?v=P3kJd3MDeuk <--Why electrons move up if the Magnetic field is Horizontal?

https://www.youtube.com/watch?v=ATFqX2Cl3-w at 0:14 <-- the Magnetic field is Horizontal but the electrons are also moving horizontally...

  • $\begingroup$ The same reason the move horizontally if the magnetic field is vertical and they are traveling parallel to the ground. $\endgroup$ – Jon Custer Sep 27 '16 at 12:28
  • $\begingroup$ This question is not very useful in its present form, since it just points to a couple of youtube videos. $\endgroup$ – Ben Crowell May 13 '18 at 22:25

All electromagnetically-charged particles experience a force due to magnetic fields that is governed by the Lorentz force $\mathbf{F}_B = q(\mathbf{v} \times \mathbf{B})$. By the nature of the cross product, this force must as a result always act perpendicular to the direction of the magnetic field; that is, no component of the force will be in the same direction as the magnetic field at any given time.

In both videos, the electrons move in a direction perpendicular to the magnetic field. Saying that the electrons are moving "horizontally" is still relatively ambiguous, as it restricts them to a plane (they still have two degrees of freedom). In the second video, the electrons move "horizontally", but this is still perpendicular to the direction of the magnetic field (ie. along the wire, while $\mathbf{B}$ is across the wire).

The electrons don't only react to the Lorentz force, though: they have to stay inside the wire (I hate to say it, but quantum mechanics!), and so moving the wire around causes the electrons to experience another force. The interplay of the electrons moving along the wires while staying within them as the wires themselves rotate/pass through the magnetic field is the foundation of the mechanics of the dynamo shown in the videos.


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