Alternators and Dynamos

• Alternators rotate in a coil in a magnetic field (or a magnet in a coil)
• The construction of alternators is like a motor
• As the coil (or magnet) in an alternator spins, a current is induced in the coil which changes direction every half turn
• Instead of a split ring commutator, alternators have slip rings and brushes so the contacts don't swap every half turn
• Alternators produce an alternating potential difference (so alternating current)
• Dynamos work in the same way as alternators apart from the difference that they have a split-ring commutator instead of slip rings
• the split-ring commutator in dynamos means that the connection is swapped every half turn to keep the current flowing the same direction
• Dynamos produce a direct current
• Oscilloscope

  used to show how the potential difference generated in a coil changes over time
• Oscilloscope lines:

  • for alternating current - a line that goes up and down, crossing the horizontal axis
  • for direct current - a line that goes up and down but stays above the horizontal axis (potential difference is always positive)
• the height of the line on an oscilloscope is the generated potential difference at that time
• Increasing the frequency of revolutions increases the overall potential difference, but it also creates more peaks on an oscilloscope
• Revolution

  One complete rotation (full turn)