Plotting magnetic fields

• Magnetic field


  The space around a magnet where a force will act on another magnet or on a magnetic material
• The Earth has a magnetic field
• A compass has a tiny magnetic needle balanced at its centre
• Due to the Earth's magnetic field

  One end of the compass always points north, and the other always points south
• North seeking pole


  The end of the compass that always points north
• South seeking pole


  The end of the compass that always points south
• Earth's magnetic field


  Like the field around a bar magnet
• Using a plotting compass

  1. Place the plotting compass next to the north pole of the magnet

  2. Put a dot on the paper to show where the needle points

  3. Move the compass forward, lining up the end of the needle with the previous dot

  4. Put a dot where the needle points

  5. Repeat until you have plotted several magnetic field lines
• Magnetic field lines


  • Closer together at the poles of the magnet
  • Further apart as you move away from the magnet
  • Indicate that the magnetic field is strongest at the poles
  • Show that magnetic field strength decreases with distance from the magnet
• Induced magnetism


  Some materials that are not magnets can be made into temporary magnets by placing them into a magnetic field
• The magnetic field induces magnetism in the material
• Materials that can be induced

  Materials that are attracted to permanent magnets such as iron
• If you take the magnet away, the paperclips lose their magnetism
• Magnetic field around a current-carrying wire

  Investigate the magnetic field around a current-carrying wire by using plotting compasses to make an image of the field lines
• A bar magnet labeled XY is hung horizontally on a piece of thread so that it is free to turn
• End marked X


  North pole
• End marked Y


  South pole
• The force is always attractive when a magnet is brought near to another magnet
• Compass needles line up with magnetic fields
• Magnetic field is always from the north pole towards the south pole
• A magnetic field is a space around a magnet where another magnet or a magnetic material feels a force
• A plotting compass consists of a small magnet balanced at its centre
• Magnetic field lines show the direction of the magnetic field