Motion of Charged Particles (CIE A Level Physics)

• A charged particle in a uniform electric field will experience a force on it that will cause it to move
  • If the charge is stationary, it will move parallel to the field lines (along or against the field lines depending on its charge)
  • If the charge is in motion (perpendicular to the field lines), it will experience a constant force and travel in a parabolic trajectory

The parabolic path of charged particles in a uniform electric field

• The direction of the parabola will depend on the charge of the particle
  • A positive charge will be deflected towards the negative plate
  • A negative charge will be deflected towards the positive plate

• The force on the particle is the same at all points and is always in the same direction
  • Note: an uncharged particle, such as a neutron experiences no force in an electric field and will therefore travel straight through the plates undeflected

• The amount of deflection depends on the following properties of the particles:
  • Mass – the greater the mass, the smaller the deflection and vice versa
  • Charge – the greater the magnitude of the charge of the particle, the greater the deflection and vice versa
  • Speed – the greater the speed of the particle, the smaller the deflection and vice versa