P15

• A magnet contains a north and South Pole, these are where the magnetic field is strongest
• Like poles repel and opposite poles attract
• What are the magnetic metals?

  Iron, Cobalt and Nickel
• What is a permanent magnet?

  A magnet with its own magnetic field that cannot be turned on or off
• What is an induced magnet?

  A material that becomes magnetised when placed in a magnetic field. These can only attract, they cannot repel
• What is a magnetic field?

  A region of space where a magnetic material will experience a force due to the magnet
• How do you draw magnetic field lines?

  Field lines always point towards the South Pole and areas where the lines are more dense (poles) represent a stronger field
• Explain electromagnetism

  When a current flows through a wire, a magnetic field is produced in concentric circles around the wire
• What is a solenoid?

  A magnet made out of current carrying wire. The wire has been coiled to make it behave like a magnet
• How can you increase the strength of a solenoid?

  • Use an Iron core
  • Increase number of coils around the core
  • Increase current flowing through the wire
• What is an electromagnet?

  A solenoid in which the insulated wire is wrapped around an iron core
• What is the right thumbs up rule?

  Point your right thumb in the direction of the current in the wire. Your fingers will then be curled in the direction of the magnetic field
• Define the motor effect

  When a magnetic field interacts with another magnetic field a force is produced
• What is Flemings Left-hand rule?

  Used to determine the direction of a force
• What doe the index finger represent in Flemings LHR?

  Field
• What does the middle finger represent in Flemings LHR?

  Direction of current
• What does the thumb represent in Flemings LHR?

  Direction of force
• Describe how an electric motor works

  • Sides of the coil experience an equal and opposite force
  • The force causes a moment and the coil rotates
  • A split ring commutator switches between the brushes every half turn
  • This reverses the current to allow continuous rotation
• What is an electric motor?

  When a current carrying wire is coiled, we can place it inside of a magnetic field and cause continuous rotation
• 2 uses of electromagnets

  Speakers and Microphones
• What is a transformer?

  A device that can change the potential difference of an alternating current
• Describe how a transformer works

  • The current carrying wire in the primary coil induces a magnetic field - magnetising the iron core
  • The direction of the induced magnetic field is constantly changing due to the alternating current
  • This changing magnetic field induces a potential difference in the secondary coil which induces a current
• What the difference between a step-up and a step-down transformer?

  Step-up transformer have more turns in the secondary coil whereas step-down transformers have more turns in their primary coil