Physics

• Magnetic field lines were introduced by Michael Faraday as a visual representation of magnetic fields
• Faraday called magnetic field lines "lines of force"
• Field line rules:

  • Field lines never cross
  • Closer the field lines, the greater the force
  • The arrow on a magnetic field line indicates the direction in which a free north pole would move
• Outcomes:

  • Aspire to: State the rules for magnetic field lines
  • Challenge to: State two methods of producing a uniformed magnetic field
  • Explain how a solenoid increases magnetic field strength compared to a current carrying wire
• Permanent magnets are permanently magnetic

  • Magnets always have a north pole
  • Field lines emanate outwards from the north pole, indicating that north-north poles repel from each other
• Permanent magnets are permanently magnetic

  • Magnets always have a south pole
  • Field lines emanate towards the south pole, indicating that north-south poles attract to each other
• The Earth has its own magnetic field which can be treated as a large permanent magnet

  • These magnetic fields protect us from charged particles which bombard Earth
• Two types of magnets:

  • Magnetism is caused by the motion of electric charges
  • Every substance is made up of tiny units called atoms, each with electrons that carry electric charges
  • The movement and alignment of electrons in different materials give rise to two types of magnetic materials: permanently magnetic and materials that can be induced to be magnetic from an external magnetic/electric field
• Electromagnetism:

  • When a charged particle moves, it creates a magnetic field
  • When a current is passed through a wire, a magnetic field is produced, creating all magnetism
• Right Hand Cork-Screw Rule:

  • Raise your right hand in the air
  • Do a thumbs up, where your thumb points in the direction of conventional current
  • Your fingers show the direction of the induced magnetic field
• Induced Magnetic Field Lines:

  • Point your thumb towards your face, your fingers wrap around in an anti-clockwise fashion
  • Point your thumb away from your face, your fingers wrap around in a clockwise fashion
• Solenoids:

  • Magnetic fields created by a current in a wire are typically low
  • To achieve large magnetic fields, such as in MRI technology, solenoids are used
  • A solenoid is a current-carrying wire looped to align magnetic fields