Alternating Current
Electricity and Magnetism

The waveform of AC on a demonstration oscilloscope

Practical Activity for 14-16 PRACTICAL PHYISCS


A simple qualitative demonstration of the varying voltage of an alternating supply.

Apparatus and Materials

  • Oscilloscope

  • Power supply, AC, low voltage variable
  • Leads, 4 mm, 2

Health & Safety and Technical Notes

Read our standard health & safety guidance


  1. Set the oscilloscope with the volts/cm switch to 1, the time-base control to 1 ms/cm, and the AC- DC switch to AC.
  2. Set the output of the power supply to 2 V (approx).
  3. Connect the AC terminals of the power supply to the input terminals of the oscilloscope. Adjust the time-base anticlockwise until four or five cycles of the waveform appear on the screen. The pattern traced on the screen should remain fixed in position.

Teaching Notes

  • This demonstration is largely to provide a talking point.
  • Point out the sine wave nature of the waveform.
  • You could show the output of other sources of AC in the same way, e.g. the output of a transformer made using C-cores and ready-made coils, or with hand-wound coils. Comparisons of the input and output voltages could be made.

This experiment was safety-tested in October 2006

  • A video showing how to use an oscilloscope:

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