P7

• Representing magnetic fields using field lines

  1. Draw arrows around the magnet from the north pole to the south pole

  2. Draw at least one straight line going into the south pole and coming out of the north pole

  3. Draw a pair of lines going into the south pole that are slightly curved and a similar pair coming out of the north pole

  4. Draw some lines that loop all the way around from the north to south
• Magnets

  • Produce a magnetic field
  • Have two poles - a north and a south
  • Surrounded by a magnetic field
• Bar magnets are the most common type of magnet, but magnets come in all shapes and sizes
• The entire earth itself is basically one huge magnet
• Field lines

  • Arrows drawn around a magnet to represent the magnetic field
  • Show where the field is and which direction it's acting in
  • Show the relative strength of the field in different places
• The denser the field lines (closer together), the stronger the magnetic field is in that area
• A compass needle is a tiny bar magnet that aligns with the field lines of a magnetic field
• Compass needle pointing towards a magnet


  Indicates the south pole of the magnet
• Interaction between two magnets with like poles


  They repel each other due to the magnetic fields
• Interaction between two magnets with opposite poles


  They attract each other as all the field lines go from north to south
• magnetic field direction

  out from north into south

  
• A = stronger magnetic field

  B = weaker magnetic field

  
• repulsion

  
• Pole A is north and pole B is north

   A and B are north because the arrows on the lines are pointing out, rather than point

  
• Types of magnets

  1. Permanent magnets

  2. Induced magnets
• Actual magnet


  Any object that produces a magnetic field
• Magnetic material


  Any object that can be influenced by a magnetic field and has the potential to become a magnet
• Common magnetic elements

  • Nickel
  • Cobalt
  • Iron
• Alloys of magnetic elements

  • Steel
• Common magnetic elements and their alloys

  • Nickel
  • Cobalt
  • Iron
  • Steel
• First letters of nickel, cobalt, iron, and steel spell 'NCIS'
• Permanent magnets


  • Produce their own magnetic field all the time
• Induced magnets

  • Only have a magnetic field temporarily, induced by a permanent magnet
• When a piece of magnetic material is put into the field of a permanent magnet


  The piece of magnetic material develops its own magnetic field with its own north and south pole, becoming an induced magnet
• Force between a permanent and induced magnet


  Always attractive
• When an induced magnet is removed from the magnetic field


  It loses its magnetism
• Types of magnetic materials

  • Magnetically soft materials
  • Magnetically hard materials
• Magnetically soft materials like nickel and iron lose their magnetism quickly
• Magnetically hard materials like steel lose their magnetism more slowly
• Electromagnetism

  1. Phenomenon whereby electric currents produce their own magnetic fields

  2. Works in ordinary wires, coils, solenoids, and electromagnets
• Magnetic field around a wire with current flowing

  Field lines are concentric circles around the wire, closest together near the wire where the magnetic field is strongest
• Right hand rule


  Use your right hand, curl it into a fist, point your thumb in the direction of the current flow, fingers curling in that direction indicate the direction of the magnetic field
• Magnetic field in a circular coil

  Field lines form ellipses, combine to form a single magnetic field through the center of the coil
• Solenoid

  Many turns of wire next to each other in one long piece, strong and uniform magnetic field inside, similar to a bar magnet outside
• Creating an electromagnet


  Using electricity to create a magnet, magnetic only when current flows through the wire, magnetic field disappears when current is turned off
• Reversing the direction of the magnetic field


  Reverse the direction of current flow to flip the direction of the magnetic field
• Ways to increase electromagnet strength

  • Increase current flow through the solenoid
  • Increase the number of turns in the coil
  • Decrease the length of the coil
  • Add an iron core to the inside of the solenoid
• A small electromagnet produces a weak magnetic field
• A current carrying wire will produce its own magnetic field
• Interaction between the magnetic field of a current carrying wire and the magnetic field of two magnets


  Results in a force on the wire pushing it out of the field