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 considered magnetic?

  Cobalt, Steel, Iron, and Nickel.
• What are the characteristics of permanent magnets?

  • Always magnetic
  • Always have poles
  • Used in speakers, compasses, and electric generators
• How are induced magnets created?

  • Materials that are magnetic but do not have fixed poles
  • Magnetism must be induced by stroking with a permanent magnet
  • Aligns all domains in the material to create a temporary magnet

  
• What happens to the magnetism of induced magnets over time?

  They lose magnetism as the domains move into random positions.

  
• In which direction do magnetic field lines point?

  From North to South.

  
• How does the strength of a magnetic field change with distance from the magnet?

  The strength decreases with distance from the magnet.

  
• What do plotting compasses show?

  The direction and shape of a magnetic field at a given point.
• What is the significance of Earth's core in relation to magnetism?

  • The core is magnetic and creates a large magnetic field around Earth
  • A freely suspended magnetic compass aligns with Earth's field lines and points North
  • Earth's magnetic North Pole is actually a magnetic South Pole
• How does current affect magnetic fields around a wire?

  Current produces a magnetic field around the wire.
• What is the "right hand rule" used for?

  To determine the direction of the magnetic field produced by a current.
• How does the strength of a magnetic field depend on current size?

  Greater current produces a stronger magnetic field.
• What happens to the magnetic field strength as the distance from the conductor increases?

  The magnetic field strength decreases with greater distance from the wire.

  
• What are the characteristics of solenoids?

  • Magnetic field shape is similar to a bar magnet
  • Coiling the wire aligns the field to form a uniform field along the center
  • An iron core increases strength
  • Individual coil fields cancel inside, producing a weaker field outside

  
• What factors affect the strength of a magnetic field in a solenoid?

  Size of current, length, cross-sectional area, number of turns, and using a soft iron core.
• What occurs when a wire carrying current is placed near a magnet?

  • The current produces a magnetic field that interacts with the magnet's field
  • The force on the conductor is equal and opposite to the force on the magnet

  
• How do two magnets interact with each other?

  They feel a magnetic force of attraction or repulsion.
• How does the magnetic field around a wire differ from the magnetic field between two magnets?

  The magnetic field around a wire is circular, while the field between two magnets is straight.

  
• How can the force on a wire in a magnetic field be visualized?

  • Fixed permanent magnets have field lines along the x-axis
  • The wire is along the y-axis with current moving up
  • The force on the wire 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 direction of force, current, and magnetic field
  • Each component is at 90⁰ to the others
  • Current is conventional current (motion of positive charge)
• What is the formula for force in terms of magnetic flux density, current, and length?


  $F =$$BIL$
• In which unit is magnetic flux density measured?

  Tesla [T]
• How does a motor operate using magnetic fields?

  • A coil of wire is placed between two permanent magnets
  • Current flows through the wire, interacting with the magnetic field
  • Causes one side of the coil to move down and the other side to move up, resulting in rotation
• How can the Left Hand Rule be used in motors?

  To verify which side of the coil moves up or down.