Magnetism and Electromagnetism

• Magnet

  Any material or object that produces a magnetic field
• Magnets

  • Have two poles: north and south
  • Surrounded by a magnetic field
• Representing magnetic fields

  1. Draw field lines from north pole to south pole

  2. Draw straight lines into south pole and out of north pole

  3. Draw curved lines into south pole and out of north pole

  4. Draw lines looping from north to south
• More dense field lines indicate stronger magnetic field
• Finding magnetic poles and field lines

  1. Use a compass

  2. Compass needle aligns with field lines

  3. Compass points towards south pole
• North poles of two magnets pushed together

  Magnets repel
• Opposite poles of two magnets brought together

  Magnets attract
• Magnetic material

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

  Any object that produces a magnetic field
• Common magnetic elements

  • Nickel
  • Cobalt
  • Iron
• Alloys of nickel, cobalt and iron also count as magnetic materials
• Permanent magnet

  Produces its own magnetic field all the time
• Induced/temporary magnet

  Only has a magnetic field temporarily when placed in the field of a permanent magnet
• When a piece of magnetic material is put into the field of a permanent magnet

  It develops its own magnetic field with north and south poles
• The force between a permanent and induced magnet

  Is always attractive
• Magnetically soft materials

  Lose their magnetism quickly, like nickel and iron
• Magnetically hard materials

  Lose their magnetism more slowly, like steel
• Electromagnetism


  The phenomenon whereby electric currents produce their own magnetic fields
• How electromagnetism works in wires, coils, solenoids, and electromagnets

  1. Imagine a wire with current flowing upwards

  2. Current produces concentric circular magnetic field lines around the wire

  3. Use right hand rule to determine direction of magnetic field

  4. If current flows in opposite direction, magnetic field reverses

  5. In a coil, magnetic fields combine to form a single field through the center

  6. In a solenoid, the magnetic field is strong and uniform inside, like a bar magnet

  7. Electromagnets can be turned on/off and reversed by controlling the current
• Electromagnets

  • They are only magnetic as long as current is flowing
  • Magnetic field disappears when current is turned off
  • Magnetic field direction can be reversed by reversing current direction
• Ways to increase electromagnet strength

  • Increase current
  • Increase number of turns in coil
  • Decrease length of coil
  • Add iron core
• Iron is a soft magnetic material that becomes an induced magnet when the solenoid is switched on, massively increasing the electromagnet's magnetic field strength
• The electromagnet loses its magnetic field as soon as the current is turned off
• Motor effect

  The idea that a current carrying wire in the presence of a magnetic field will experience a force
• Finding the direction and strength of the force on a current carrying wire in a magnetic field

  1. Determine direction of magnetic field

  2. Determine direction of current in wire

  3. Use Fleming's left-hand rule to find direction of force

  4. Calculate force using equation F=BIL
• Fleming's left-hand rule

  • Point thumb up for direction of force, first finger for direction of magnetic field, second finger for direction of current
• Magnetic flux density

  Magnetic field strength, measured in Teslas
• Force (F) = Magnetic flux density (B) x Current (I) x Length of wire (L)