Magnetism

• Permanent magnet


  Produces its own magnetic field
• Induced magnet


  • Becomes a magnet when placed in a magnetic field
  • Always causes a force of attraction
• Plotting a magnetic field around a magnet using a compass

  1. Place compass at pole

  2. Mark start and end of compass

  3. Place compass at drawn end of arc

  4. Repeat and use these to draw a line of force
• Solenoid


  • Magnetic field is strong
  • Magnetic field is uniform
  • Magnetic field has same shape as a bar magnet
• Solenoid has a stronger magnetic field than an ordinary wire

  Field lines around each loop of wire line up with each other increasing strength
• Fleming's left-hand rule


  • Thumb represents force direction
  • First finger represents magnetic field direction
  • Second finger represents current direction
• How a loudspeaker works

  1. Coil of wire around a permanent magnet

  2. Coil of wire attached to a diaphragm

  3. Alternating current in the coil of wire

  4. Causes the wire and therefore diaphragm to move forwards and backwards creating sound waves
• How a microphone works

  1. Coil of wire around a permanent magnet

  2. Coil of wire attached to a diaphragm

  3. Sound waves cause diaphragm to move forwards and backwards

  4. Causing coil of wire to move forwards and backwards in magnetic field inducing an alternating current in the coil of wire
• How a transformer works

  1. Alternating current in the primary coil creates an alternating magnetic field around the primary coil

  2. Which transfers to the (soft) iron core

  3. Which induces an alternating potential difference in the secondary coil
• How a motor works

  1. Alternating current in the motor coil of wire creates an alternating magnetic field

  2. That is repelled by the motor's permanent magnet

  3. Each half turn the split ring commutator reverses the current direction

  4. Which reverses the magnetic field direction
• How a generator works

  1. A coil of wire rotates in a magnetic field

  2. Inducing an alternating current in the coil of wire

  3. Slip rings and brushes carry the induced current out