Electric Motors

• Electric motors


  Use the motor effect to get them (and keep them) moving
• This is one of the favourite exam topics of all time, Read it. Understand it. Learn it.
• How an electric motor works

  1. Current-carrying coil of wire rotates in a magnetic field

  2. Forces act on the two side arms of the coil

  3. Coil is on an axle and the forces act one up and one down, causing it to rotate

  4. Split-ring commutator swaps the contacts every half turn to keep the motor rotating in the same direction
• Direction of the motor can be reversed


  By swapping the polarity of the DC supply (reversing the current) or swapping the magnetic poles over (reversing the field)
• Direct current (DC)


  Current that only flows in one direction
• Using Fleming's left-hand rule


  To work out which way the coil will turn
• Determining coil rotation direction

  • Draw in current arrows
  • Use Fleming's left-hand rule on one branch
  • Draw in direction of force (motion)
• In the example, the coil is turning anticlockwise