P13: electromagnetic waves

• Magnetism


  A property of certain materials that produces a magnetic field and attracts or repels other magnetic materials
• Permanent magnets


  • Produce a magnetic field that cannot be turned off
  • Examples: bar magnet, Earth
• Magnetic elements


  • Copper
  • Iron
  • Nickel
• Induced magnetism


  When a magnetic material becomes magnetised when placed in a magnetic field
• Opposite poles of magnets


  Attract each other
• Like poles of magnets

  Repel each other
• Electromagnet


  A magnet created by running an electric current through a coil of wire wrapped around a magnetic material
• Electromagnets


  • Strength can be increased by increasing the number of coils, the current, or using a more magnetic material
  • Can be turned on and off
• Motor effect


  The force experienced by a current-carrying wire in a magnetic field, causing it to spin
• Using Fleming's left-hand rule to determine the direction of the motor effect

  1. Point thumb in direction of force

  2. Point index finger in direction of magnetic field

  3. Point middle finger in direction of current

  4. Thumb shows direction of force
• Generator effect


  Using a changing magnetic field to induce an electric current in a wire
• Changing magnetic field


  Induces a current in a wire
• Transformer


  A device that uses electromagnetic induction to increase (step-up) or decrease (step-down) the voltage in an electrical circuit
• How transformers work


  1. Alternating current in primary coil creates alternating magnetic field in iron core

  2. Alternating magnetic field induces alternating current in secondary coil
• Step-up transformer


  Increases the voltage from the primary to secondary coil
• Step-down transformer


  Decreases the voltage from the primary to secondary coil
• Transformers are used to efficiently transmit electricity over long distances by stepping up the voltage to reduce energy losses