The motor effect

• What does passing an electric current through a wire produce?

  A magnetic field around the wire
• What happens when a current-carrying wire is placed in a magnetic field?

  The two magnetic fields interact and exert a force
• What is the term for the interaction between a current-carrying wire and a magnetic field?

  The motor effect
• What is required for a wire to experience the full force in a magnetic field?

  The wire must be at 90° to the magnetic field
• What happens if the wire runs parallel to the magnetic field?

  It won’t experience any force at all
• At what angles will the wire feel some force?

  At angles between 0° and 90°
• In which direction does the force act in relation to the magnetic field and current?

  At right angles to both the magnetic field and current
• How can the direction of the force be demonstrated practically?

  • Apply current to rails inside a horseshoe magnet
  • A bar rolls along the rails
• What happens to the magnitude of the force with an increase in magnetic field strength?

  The force increases with magnetic field strength
• How does the amount of current affect the force on the conductor?

  The force increases with the amount of current
• What factors determine the force acting on a conductor in a magnetic field?

  1. Magnetic flux density (T)
  2. Size of the current (I)
  3. Length of the conductor in the field
• What is the equation to find the force acting on a conductor at 90° to the magnetic field?

  F = BIL
• What does each variable in the equation F = BIL represent?

  F is force, B is magnetic flux density, I is current, L is length
• How can you determine the direction of the force using Fleming’s left-hand rule?

  1. First finger: direction of the magnetic field
  2. Second finger: direction of the current
  3. Thumb: direction of the force (motion)
• What happens to the direction of the force if the current or magnetic field is reversed?

  The direction of the force will also be reversed
• How can Fleming’s left-hand rule be useful in exams?

  • Helps determine the direction of force
  • Simplifies problem-solving in magnetic field questions
• What should you do to find the direction of the force acting on a wire in a magnetic field?

  Use Fleming’s left-hand rule
• What is the first step in using Fleming’s left-hand rule?

  Point your first finger in the direction of the field
• What is the second step in using Fleming’s left-hand rule?

  Point your second finger in the direction of the current
• What does your thumb indicate when using Fleming’s left-hand rule?

  The direction of the force (motion)
• What should you do in an exam when asked about the direction of force on a wire?

  Draw in current arrows and use Fleming’s LHR
• What is the mark allocation for finding the direction of the force acting on the wire?

  1 mark