Motor Effect

• When a current flows through a conducting wire a magnetic field is produced around the wire
• The strength of the magnetic field around a wire depends on the current through the wire and the distance from the wire
• Shaping a wire to form a solenoid increases the strength of the magnetic field created by a current through the wire

  
• The magnetic field inside a solenoid is strong and uniform
• Adding an iron core increases the strength of the magnetic field of a solenoid
• The magnetic field around a solenoid has a similar shape to that of a bar magnet
• An electromagnet is a solenoid with an iron core
• Ways to increase the strength of a magnetic field produced by a solenoid

  • Increase size of the current
  • Increase number of turns of the coil
  • Placing and iron core inside
• When a conductor carrying a current is placed in a magnetic field the magnet producing the field and the conductor exert a force on each other. This is called the motor effect
• For a conductor at right angles to a magnetic field and carrying a current:

  Force = Magnetic flux density × Current × Length

  $F =$$BIl$

  • Force ( F ) in newtons ( N )
  • Magnetic flux density ( B ) in tesla ( T )
  • Current ( I ) in amperes ( A )
  • Length ( l ) in metres ( m )
• A coil of wire carrying a current in a magnetic field tends to rotate. This is the basis of an electric motor
• Loudspeakers and headphones use the motor effect to convert variations in current in electrical circuits to the pressure variations in sound waves
• Flemings left hand rule

  A) Movement

  B) Field

  C) Current