permanent and induced magnets

• Magnet


  An object capable of exerting a magnetic force
• Magnet


  • Has two poles: north pole and south pole
• North pole


  In a magnet, the end that is attracted to the Earth's magnetic north pole
• South pole


  In a magnet, the end that is attracted to the Earth's magnetic south pole
• Magnetic force is strongest near the magnet's poles
• Like poles (N-N or S-S)

  Repel
• Unlike poles (N-S or S-N)

  Attract
• Magnetic forces


  Non-contact forces - magnets affect each other without touching
• Magnetic materials


  Iron, steel, nickel and cobalt - able to be magnetised or attracted to a magnet
• Permanent magnet


  • Produces its own magnetic field
  • Magnetic field cannot be turned on and off - it is there all the time
• Permanent magnets


  • Bar magnets
  • Horseshoe magnets
• Induced magnet


  • A temporary magnet, made from a magnetic material placed in a magnetic field
  • The induced magnetism is lost when moved out of the magnetic field
• Induced magnets are only attracted by other magnets, they are not repelled
• Induced magnets lose most or all of their magnetism when they are removed from the magnetic field
• Testing for magnetism


  • A permanent magnet can attract or repel another permanent magnet
  • A permanent magnet can attract a magnetic material (but not repel it)
• You can only show that an object is a permanent magnet by checking if it repels another magnet
• Magnetic field


  Area surrounding a magnet that can exert a force on magnetic materials
• Detecting magnetic fields


  1. Use a magnetic compass

  2. Place the plotting compass near the magnet on a piece of paper

  3. Mark the direction the compass needle points

  4. Move the plotting compass to many different positions in the magnetic field, marking the needle direction each time

  5. Join the points to show the field lines
• The needle of a plotting compass points to the south pole of the magnet
• The Earth has a magnetic field produced by its iron and nickel core
• Magnetic field lines


  • They never cross each other
  • The closer the lines, the stronger the magnetic field
  • The lines have arrowheads to show the direction of the force exerted by a magnetic north pole
  • The arrowheads point from the north pole of the magnet to its south pole
• The diagram shows the magnetic field around a bar magnet