Unit 9

• What did the ancient Greeks discover about lodestone?


  It attracts small pieces of iron
• What is lodestone?


  An iron-containing mineral that is naturally magnetic
• How does lodestone exert its magnetic force?


  It exerts a non-contact magnetic force on iron pieces
• What are some examples of artificial magnets?


  • Horseshoe magnets
  • Bar magnets
  • Circular magnets
• What is magnetism described as?


  An invisible force that pulls magnetic metal objects towards a magnet
• What are the two poles of a magnet?

  North pole and South pole
• What happens when different poles of magnets are brought together?


  They attract each other
• What occurs when the same poles of magnets are brought together?


  They repel each other
• Are all metals magnetic?


  No, only some metals are magnetic
• Is aluminium a magnetic metal?


  No, aluminium is not magnetic
• What is a paper clip made of?


  A magnetic material
• Is a knife made of steel magnetic?


  Yes, steel is magnetic
• Is a pencil made from a magnetic material?


  No, a pencil is not made from a magnetic material
• Is a rubber ball magnetic?

  No, a rubber ball is not magnetic
• Is a screw made from iron magnetic?


  Yes, a screw made from iron is magnetic
• What are the different types of magnets mentioned?

  • Horseshoe magnets
  • Bar magnets
  • Circular magnets
• What do all magnets have?


  A North pole and a South pole
• What do different poles of magnets do?


  Different poles attract
• What do poles that are the same do?


  Poles that are the same repel
• What happens to the domains in magnetic material when it is not magnetized?


  The domains point in lots of different directions
• What occurs when magnetic material is magnetized?


  The domains line up
• What happens when electricity flows through a straight wire?


  A magnetic field is formed around the wire
• Why are electromagnets preferred over permanent magnets?


  Electromagnets can easily be turned on and off
• What are some uses of electromagnets?


  • Levitation in MEGLEV trains
  • Starting and moving cars
  • Operating relays
  • X-ray machines
  • Electric bells
  • MRI scanners
  • Circuit breakers
  • Magnetic storage in TVs and computers
• What is an electromagnet?


  A temporary magnet created using electricity
• How does the strength of the magnetic field relate to the current in the wire?


  The stronger the current, the stronger the magnetic field
• How fast does the MEGLEV train float?


  375 mph
• How do powerful magnets on the tracks affect the MEGLEV train?

  They repel the train, eliminating friction
• What happens to the magnetic field when the current stops flowing?


  There is no magnetic field
• What is a solenoid?


  A long thin spiral of wire used to produce a magnetic field
• What is the role of an electromagnetic switch in cars?


  It safely controls the large current from the car battery
• What is a relay?


  A relay uses a small current in one circuit to operate a switch in another circuit
• What happens when the switch in a relay is closed?


  The coil becomes an electromagnet and attracts two pieces of iron
• How does the magnetic field of a solenoid compare to that of a bar magnet?


  The magnetic field of a solenoid is very similar to that of a bar magnet
• What happens to the magnetic fields in a solenoid when current flows through it?


  The small magnetic fields from each turn of the coil add together to create a stronger overall magnetic field
• Why is a relay used in X-ray machines?


  To safely switch on the machine due to high potential difference
• What are the steps involved in using a relay for an X-ray machine?


  1. Close the switch in one part of the circuit
  2. Coil becomes an electromagnet
  3. Two pieces of iron attract each other
  4. Current flows, turning on the X-ray machine
• How can the direction of the magnetic field inside a loop of wire be determined?


  By curling the fingers of the right hand in the direction of the current; the thumb points in the direction of the magnetic field
• What are the two manners in which magnetism can occur?

  Ferromagnetism and electromagnetism
• What is a magnetic relay?


  A switch operated by an electromagnet