Magnetic Force on a Charge (Edexcel IGCSE Physics)

Spec point — 6.11P · know that there is a force on a charged particle when it moves in a magnetic field as long as its motion is not parallel to the field (physics only)

Magnetic force on a charge

• When a current-carrying wire is placed in a magnetic field, it will experience a force if the wire is perpendicular

  • This is because the magnetic field exerts a force on each individual electron flowing through the wire

• Therefore, when a charged particle passes through a magnetic field, the field can exert a force on the particle, causing it to deflect

  • The force is always at 90 degrees to both the direction of travel and the magnetic field lines
  • The direction can be worked out by using Fleming's left-hand rule

The electron experiences a force upwards when it travels through the magnetic field between the two poles. Remember that conventional current flows in the opposite direction to electrons.

• If the particle is travelling perpendicular to the field lines:

  • It will experience the maximum force

• If the particle is travelling parallel to the field lines:

  • It will experience no force

• If the particle is travelling at an angle to the field lines:

  • It will experience a small force

Exam Hint Remember that the direction of current flow in Fleming's Left-Hand Rule is from positive to negative. This means it is in the opposite direction to the direction of travel of an electron (which is negatively charged)