Investigation of the motion of charged particles in magnetic fields yields:

 

  1. Magnitude of the magnetic force is proportional to the charge q and speed v of the particle.
  2. Magnitude and direction of magnetic force depend on the velocity of the particle and on the magnitude and direction of the magnetic field.
  3. When a charged particle moves parallel to the magnetic field vector, the magnetic force on the charge is zero.
  4. When the velocity vector makes an angle q with the magnetic field, the magnetic force acts in a direction perpendicular to both v and B; that is, F is perpendicular to the plane containing v and B.
  5. The magnetic force on a positive charge is in the direction opposite the direction of the force on a negative charge moving in the same direction.
  6. If the velocity vector make an angle q with the magnetic field, the magnitude of the magnetic force is proportional to sin q.

 

 

or

 

 

Comparison of E and B forces

 

  1. Electric force is always in the direction of the electric field.  Magnetic force is perpendicular to the magnetic field.
  2. Electric force acts on a charged particle independent of the particle’s velocity.  Magnetic force acts on a charged particle only when the particle is in motion.
  3. Electric force does work in displacing a charged particle.  Magnetic force associated with a steady magnetic field does no work when a particle is displaced.