Graphs of Potential Difference in the Coil (AQA GCSE Physics)

Oscilloscopes

• A device called an oscilloscope is used to show how the potential difference generated in the coil changes over time
• It will produce a line, called a trace, on a screen
• The vertical axis of the trace is the generated potential difference
  • The higher the line, the greater the amount of potential difference induced

• The horizontal axis of the trace is time
  • This allows the variation in potential difference against time to be shown

Trace of generated potential difference against time on an oscilloscope

Alternating Potential Difference Trace on an Oscilloscope

• An alternator consists of a rotating magnet next to (or inside) a coil

Alternating potential difference trace showing the position of the magnet relative to the coil

• When the magnet is in position 1 the magnetic field lines of the magnet do not cut the coil
  • This means that there is no potential difference induced in the coil

• When the magnet is in position 2 the magnetic field lines of the magnet are at 90^o to the coil
  • This means that there will be maximum potential difference induced in the coil

• When the magnet is in position 3 the magnetic field lines of the magnet do not cut the coil
  • This means that there is no potential difference induced in the coil

• When the magnet is in position 4 the magnetic field lines of the magnet are at 90^o to the coil
  • This means that there will be maximum potential difference induced in the coil
  • As the poles of the magnet are reversed compared to position 2 the induced potential difference will also be in the opposite direction compared to position 2
  • This means that the trace is negative

Direct Potential Difference Trace on an Oscilloscope

• A dynamo consists of a coil, which is rotated by a mechanical process, inside a magnetic field

Direct potential difference trace showing the position of the coil relative to the magnetic field

• When the coil is in position 1 the magnetic field lines of the magnet do not cut the coil
  • This means that there is no potential difference induced in the coil

• When the coil  is in position 2 the magnetic field lines of the magnet are at 90^o to the coil
  • This means that there will be maximum potential difference induced in the coil

• When the coil is in position 3 the magnetic field lines of the magnet do not cut the coil
  • This means that there is no potential difference induced in the coil

• When the coil is in position 4 the magnetic field lines of the magnet are at 90^o to the coil
  • This means that there will be maximum potential difference induced in the coil
  • The trace will remain positive because there has been no change to the direction of the magnetic field