Electromagnetism

• Motor


  • Can be used to make a motor spin
  • Spin faster by using a coil with more turns, larger current, stronger magnets, or larger coil area
  • Change direction by changing direction of current or reversing field
• Split ring


  Part of a motor
• Coil of wire


  Part of a motor
• Carbon brush


  Part of a motor
• Magnet


  Part of a motor
• Motor operation


  1. Wire carrying current through magnetic field has force acting on it

  2. Direction of force given by Fleming's Left Hand Rule

  3. Size of force calculated using F=BIl
• Fleming's Left Hand Rule

  Thumb = Force/Motion, Middle finger = Current, First Finger = Field, From N to S
• Generator operation


  1. Wire moved through magnetic field generates current

  2. Direction of current given by Fleming's Right Hand Rule

  3. Larger current by more coil turns, stronger magnets, larger coil area

  4. Faster turning increases current but also frequency
• Fleming's Right Hand Rule

  Thumb = Force/Motion, Middle finger = Current, First Finger = Field, From N to S
• Magnetic field


  • Area where magnetic force is felt
  • Strength shown by closeness of lines
  • Wire carrying current creates magnetic field
  • Larger current, more coil turns create stronger field but reversing current reverses field direction
• Transformer


  • Uses magnetic field to step up or step down voltage
  • Primary coil creates alternating magnetic field
  • Core strengthens and connects field to secondary coil
  • Alternating field in secondary coil generates alternating current
  • Ratio of turns and voltage given by V1/V2 = N1/N2
• The coil with the most turns will have the higher voltage, e.g. in a step-up transformer the secondary coil has the most turns to increase the voltage