CIE A Level Physics (9702) 2019-2021

Revision Notes

25.3.4 Deflection of Charges Particles in E and B Fields

Deflection of Particles in E and B Fields

  • Forces due to electric (E) and magnetic (B) fields will influence the motion of charged particles
  • A charged particle will experience a force in an electric field that will cause it to move
    • If the particle remains still in an electric field, it will move parallel to the field lines (direction depending upon its charge)
    • This is because the electric force is parallel to the particle’s velocity and the electric field lines
    • If the particle is in motion in an electric field, it will move in a parabolic trajectory

  • A charged particle will only experience a force in a magnetic field if it is already moving
    • If a particle is in motion in a magnetic field, it will move in circular motion
    • This because the magnetic force is perpendicular to the velocity of the charged particle and the magnetic field lines
    • The magnetic force is equal to the centripetal force on the particle

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