I know that the energy comes from the magnetic field, but if the electron is moving, then how does the magnet give the electron energy? If the magnet is moving, then the kinetic energy of the magnet is given to the electron via the magnetic field. But what about when the electron is moving? Where is the energy coming from? Does it come from the magnet? If so, does that make the magnet weaker?

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    $\begingroup$ If you are talking about an electron moving in an external magnetic field, then the classical force on the electron is $\vec{F} = q \vec{v} \times \vec{B}$. This force does not do work on the electron since it is perpendicular to the velocity. So the energy of the electron does not change. $\endgroup$ Jun 14, 2022 at 13:04
  • $\begingroup$ How does the Lorentz force work $\endgroup$ Jun 15, 2022 at 3:39

1 Answer 1


A magnetic field does not change the energy of an electron. It may change its direction, but the magnetic force is always perpendicular to the velocity, so it never changes the speed and therefore never changes the kinetic energy.

  • $\begingroup$ that is true, but I will request you to include the word Work done in your answer to get much more clarification about what do you actually mean to say the velocity and magnetic force are perpendicular. If the displacement vector is perpendicular to the force then the dot product must be zero. So no change in energy. $\endgroup$ Jun 15, 2022 at 0:43

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