topic p7- magnetism and electromagnetism

• what is a magnetic field?

  a region around a magnet where a force acts on another magnet or magnetic material
• how can you represent a magnetic field?

  using magnetic field lines, which show the direction and strength of the field

  closer lines mean a stronger field
• what happens when opposite poles are brought together?

  they attract (north and south)
• what happens when the same poles are brought together?

  they repel (north and north or south and south)
• name three magnetic materials

  iron, cobalt, nickel
• what is the difference between a permanent and an induced magnet?

  permanent magnets produce their own magnetic field, while induced magnets only become magnet when in a magnetic field
• what causes the earth's magnetic field?

  movements of molten iron in the earth's outer core
• what does a compass show?

  the direction of the earth's magnetic field (it points to magnetic north)
• what happens when a current flows through a wire?

  a magnetic field is created around the wire
• how can the magnetic field around a wire be made stronger?

  increase the current or coil the wire into a solenoid
• what is a solenoid?

  a coil of wire that produces a strong and uniform magnetic field when current flows through it
• how can an electromagnet be made stronger?

  increase the current, add more turns to the coil, or use a soft iron core
• what is the motor effect?

  when a current-carrying wire in a magnetic field experiences a force
• what affects the size of the force in the motor effect?

  the size of the current, the strength of the magnetic field, and the angle between the wire and field (force is maximum when perpendicular)
• what is fleming's left-hand rule?

  a rule to predict the direction of force:

  • thumb= motion (force)
  • first finger= field
  • second finger=current
• how does an electric motor work?

  a current in a coil within a magnetic field causes forces on opposite sides of the coil making it rotate
• how can the direction of rotation in a motor be reversed?

  reverse the current of reverse the magnetic field
• what is the right-hand thumb rule?

  a method to determine the direction of the magnetic field around a current-carrying wire
• how do you use the right-hand thumb rule?

  • point your thumb in the direction of the current
  • your fingers curl in the direction of the magnetic field

  this shows the circular field lines around the wire