Welcome to practical physicsPracticle physics - practical activities designed for use in the classroom with 11 to 19 year olds

The waveform of AC on a demonstration oscilloscope


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

Apparatus and materials


Power supply, AC, low voltage variable

Leads, 4 mm, 2

Health & Safety and Technical notes

Oscilloscopes contain high voltages and often have ventilation holes which allow access to points which are 'hazardous live'. Warn classes not to poke anything through holes in the case.

A video available at the National STEM Centre eLibrary shows how to use an oscilloscope.


a 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.

b Set the output of the power supply to 2 V (approx).

c 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.

Oscilloscope and power supply

Teaching notes

1 This demonstration is largely to provide a talking point. 

2 Point out the sine wave nature of the waveform.

3 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-checked in October 2006

Related guidance

Why teach about AC?