Topic 7 Magnetism and Electromagnetism

• What is a permanent magnet?

  A magnet that always produces a magnetic field
• What is an induced magnet?

  A material that becomes magnetised when placed in a magnetic field.
• How can we visualise magnetic fields?

  Using mini compasses or iron fillings placed in a magnetic field to draw the field lines going from the North pole to the South
• What are the 3 common metals for magnets?

  Iron, cobalt and nickel.
• How do magnetic poles work?

  Opposite poles will always attract each other while like poles will always repel
• What is the motor effect?

  The motor effect is the phenomenon where a current-carrying conductor experiences a force when placed in a magnetic field.
• How do we calculate force?

  Force = magnetic flux density x current x length

  • F = BIL
• What do motors use?

  The motor effect: both sides of a coil experience a force in opposite directions, and it turns
• How can we increase the speed of a motor?

  • Add more turns to coil
  • Increase p.d./current
  • Use stronger magnet
• What does a split-ring commutator do?

  Reverses the direction of current in a DC motor.
• How do loudspeakers work?

  Using the motor effect, a current is sent from a source (e.g. a phone) which causes the coil and speaker cone to vibrate, producing sound waves
• What is the generator effect?

  The generator effect is the phenomenon where a conductor moving through a magnetic field generates an electric current.
• How can we increase the output of a dynamo or generator?

  • Add more turns to coil
  • Use stronger magnet
• What is a microphone?

  An 'inverted' loudspeaker. Sound waves cause the coil to oscillate past magnet, which induces signal