Force on a Current-Carrying Conductor (CIE IGCSE Physics: Co-ordinated Sciences (Double Award))

Extended tier only

• A current-carrying conductor produces its own magnetic field
  • When interacting with an external magnetic field, it therefore will experience a force

• A current-carrying conductor will only experience a force if the current through it is perpendicular to the direction of the magnetic field lines
  • A simple situation would be a copper rod placed within a uniform magnetic field
  • When current is passed through the copper rod, it experiences a force which makes it move

A copper rod moves within a magnetic field when current is passed through it

• Two ways to reverse the direction of the force (and therefore, the copper rod) are by:
  • reversing the direction of the current
  • reversing the direction of the magnetic field

Extended tier only

• The direction of the force (aka the thrust) on a current-carrying wire depends on the direction of
  • the current
  • the magnetic field

• The direction of the force (or thrust) can be worked out by using Fleming's left-hand rule:
  • the thumb points in the direction of the force, or thrust, on the conductor
  • the first finger points in the direction of the magnetic field
  • the second finger points in the direction of current flow (from positive to negative)

Fleming’s left-hand rule can be used to determine the directions of the force, magnetic field and current

• All three will be perpendicular to each other in Fleming's left-hand rule questions
  • This means that sometimes the force could be into and out of the page (in 3D)