Magnetism 4.1

• Magnetism is an example of a non contact force
• Opposite poles attract ,like poles repel
• what metals are magnetic

  Iron, cobalt, nickel and steel (an alloy which contains iron )
• For 2 repelling bar magnets

  Like poles will repel

  no field
• Two attracting bar magnets

  Strong magnetic field pushes poles together

  opposite poles attract

  uniform field
• How to test for magnetic material

  1. if the object can be repelled by the known magnet it is a magnet
  2. If the object can only be attracted and not repelled, its a magnetic material
• What are the two types of magnets

  Induced and permanent
• Permanent magnets

  1. Made out of permanent magnetic material eg. steel
  2. Will produce its own magnetic field and won’t lose magnetism
• Induced magnetic

  1. when the magnetic material is placed in a magnetic field , the material temporarily turns into a magnet
  2. Magnetic material will always be attracted to permanent magnet
  3. When the magnetic material is removed from the magnetic field it will lose most of its magnetism
• What is a magnetic field

  The region around a magnet where a force acts on another magnet or on a magnetic material (iron, steel, cobalt and nickel)
• What do magnetic field lines represent

  The strength and direction of a magnetic field
• How do field lines link to magnetic field

  Close field lines —> magnetic field will be strong

  Distant field lines —> magnetic field will be weak
• What are the rules of field lines

  1. The direction of field lines must go from north to south
  2. They must never touch or cross other field lines
• What is a uniform bar magnet

  A uniform bar magnet is one that has the same strength and direction at all points
• How must you draw a uniform bar magnet

  1)There must be equal spacing to show the magnetic field has the same strength. 2)There must be an arrow going from North to South to show they are going in the same direction. 3)The field lines must be the same distance apart to indicate that the field strength is the same at every point between the poles
• In the absence of a magnet/magnetic material , a magnetic compass will always point North , this is proof the Earth’s core is magnetic and creates its own magnetic field
• Geographical North Pole = magnetic South Pole (magnetic field line point into the pole )

  Geographical South Pole = magnetic North Pole ( magnetic field line point out of the pole )
• A conducting wire is any wire that has current flowing through it
• A magnetic field around a wire is made up of concentric circles and circular field lines indicates the magnetic field has no poles.
• As the current increases, the magnetic field increases (shown by more concentrated field lines )
• As the distance from the conductor increases, the magnetic field decreases ( shown by less concentrated field lines )
• To increase the strength of the magnetic field around the wire it should be coiled to form A solenoid
• The magnetic field inside a solenoid is strong and uniform
• In a solenoid, if current is traveling clockwise its the South Pole
• In a solenoid if current is traveling anticlockwise it is the North Pole
• No current = no magnetic field
• How to increase the strength in solenoid magnetic field

  1. Increasing the size of current flowing through the wire
  2. Increasing the number of coils
  3. Adding an iron core through the Centre of the coils
• Why would adding a soft iron core increase the strength in solenoid magnetic field

  Because the soft iron core would become an induced magnet ,when current is flowing through the coils the magnetic field from the solenoid as well as the soft iron core would result in a much stronger magnet .