4.2.7 electromagnetic induction 2

• If a wire is moving downwards into a horseshoe magnet

  • a potential difference is induced in the wire and an electric current flows through the wire
  • a force will push the wire upwards, opposing the downwards movement of the wire that induced the potential difference
• If a wire is moving upwards out of a horseshoe magnet

  • a potential difference is induced in the wire and an electric current flows through the wire
  • the force on the wire due to the induced potential difference would push it downwards
• Features of the motor effect

  • The force created acts in the opposite direction to the action which induced the potential difference
• Features of the motor effect

  • it creates a force when potential difference is induced
• When a p.d is induced in a wire, it creates a force acting in the opposite direction to the action that induced the p.d - this is due to the motor effect.
• • The diagram below shows the positions of the coil that give the peaks and zeros in the potential difference.
  • When the coil is in position Y, the top and bottom edge of the coil (sides AB and CD) are moving parallel to the magnetic field lines.
  • The coil doesn’t cut across any magnetic field lines so there is no induced p.d.
  • When the coil is in position Z, the sides AB and CD of the coil are moving perpendicular (at 90 degrees) to the magnetic field lines.
  • At this point the coil cuts across the most field lines, so the magnitude (size) of the induced p.d is highest.

  
• The magnitude of induced potential difference is affected by

  • the angle between the coil and the magnetic field lines
  • the number of field lines that the coil cuts through
• Induced p.d is highest when the edges of the coil are moving at a 90 degree angle to the magnetic field lines.
• In which direction does a force induced by the motor effect run?

  In the opposite direction to the inductive force
• Voltage output of an AC generator

  • The diagram below shows the graph of how the potential difference induced in an AC generator varies with time, alongside the position of the coil generator at that time.