Physics - Topic 12 - Magnetism and the Motor Effect

• What happens when like poles of magnets are brought together?

  They repel each other.
• What happens when opposite poles of magnets are brought together?

  They attract each other.
• Which materials are typically magnetic?

  Cobalt, Steel, Iron, and Nickel.
• What are permanent magnets and their uses?

  • Always magnetic and have fixed poles
  • Used in:
  • Speakers
  • Compasses
  • Electric generators
• What are induced magnets?

  Materials that become magnetic only when magnetism is induced.
• How can you create a temporary magnet from an induced magnet?

  By stroking it with a permanent magnet.
• What happens to the domains in an induced magnet when it loses magnetism?

  They move into random positions.

  
• In which direction do magnetic field lines point?

  From North to South.
• How does magnetic field strength change with distance from the magnet?

  It decreases with distance from the magnet.
• What do plotting compasses show?

  The direction and shape of a magnetic field at a given point.
• Why does a freely suspended magnetic compass point North?

  Because it aligns itself with Earth's magnetic field lines.
• Why is Earth's magnetic North Pole actually a magnetic South Pole?

  Because like poles repel, so the compass's north pole aligns with it.
• What does current produce around a wire?

  A magnetic field.
• What dictates the direction of the magnetic field produced by a current?

  The "right hand rule."

  
• How does the strength of a magnetic field depend on current size?

  Greater current produces a stronger magnetic field.
• How does distance from a conductor affect magnetic field strength?

  Greater distance results in a weaker field.
• What happens when a wire carrying current is near a magnet?

  The current's magnetic field interacts with the magnet's field.
• What are the characteristics of solenoids?

  • Magnetic field shape similar to a bar magnet
  • Coiling wire aligns the field
  • Iron core increases strength
  • Individual coil fields cancel inside
  • Factors affecting strength:
  • Size of current
  • Length
  • Cross-sectional area
  • Number of turns (coils)
  • Using a soft iron core
• How does the magnetic field around a wire differ from that between two magnets?

  The wire's field is circular, while the magnets' field is straight.
• How do two magnets interact?

  They feel a magnetic force of attraction or repulsion.
• How can you visualize the force felt on a wire in a magnetic field?

  It is at right angles to both the current direction and magnetic field lines.

  
• What is Fleming's Left Hand Rule used for?

  • To determine the unknown factor among force, current, and magnetic field
  • Each component is at 90⁰ to the others
  • Current is conventional current (positive charge motion)
• What is the formula for force in a magnetic field?

  Force = (magnetic flux density) × (current) × (length)
• How is magnetic flux density measured?

  In Tesla [T].
• How do motors operate using magnetic fields?

  • A coil of wire is placed between two permanent magnets
  • Current flows through the wire
  • Magnetic field produced interacts with the magnets
  • Causes one side of the coil to move down and the other side to move up, resulting in rotation