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Electric and Magnetic field

  1. May 2, 2015 #1
    Will a static electron be influenced by a magnetic field.
  2. jcsd
  3. May 2, 2015 #2


    Staff: Mentor

    What do you mean by static electron?

    Do you mean a stationary electron relative to a static magnetic field like an ordinary magnet?

    The force on the electron is: F = qv x B where q is the charge of the electron and v is its velocity and B is the magnetic field vector.

    So ask yourself what is the force on the electron if it's not moving and that should answer your question.
  4. May 2, 2015 #3


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    Well, if there's only a magnetic field in the restframe of the electron, there'll be no force on the electron (see the previous posting). But if the magnetic field is time-dependent there's also an electric field due to Faraday's Law,
    $$\frac{1}{c} \partial_t \vec{B}+\vec{\nabla} \times \vec{E}=0.$$
    Then, of course the force on the electron is the full Lorentz force,
    $$\vec{F}=q \left (\vec{E}+\frac{\vec{v}}{c} \times \vec{B} \right ).$$
    So then it will be affected. You have to always look at both the electric and the magnetic field. In fact, electric and magnetic fields are just a split of the one and only electromagnetic field into components with respect to an arbitrary inertial reference frame.

    NB: I always use Heaviside-Lorentz units, because they are the most natural ones for electromagnetism.
  5. May 2, 2015 #4
    May we say, therefore, that the electrons in a receiving antenna move only in response to the E-field of a passing wave?
  6. May 2, 2015 #5


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    No, because when the electron moves, there's also a force due to the magnetic field, as written above.
  7. May 6, 2015 #6
  8. May 6, 2015 #7


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    The charge produces of course a field, and in principle you have to take it into account. This is the socalled "radiation reaction" and is a tremendously difficult problem, which has not a full resolution for a point partice within classical electrodynamics. Have a look at the usual textbooks (Landau Lifshitz vol. II, Jackson etc.).
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