Physics · Study 019
Lissajous Scope
An oscilloscope in XY mode: one sine wave drives the beam sideways, another drives it up and down, and Lissajous figures appear.
What you're looking at
The horizontal position of the beam follows one sine wave and the vertical position follows another. When the two frequencies form a simple ratio such as 2 to 3, the beam retraces a closed knot. A slow phase drift between them makes the figure appear to rotate in three dimensions.
The idea behind it
Before digital counters, engineers used these figures to compare frequencies: feed in a known signal and an unknown one, then count the lobes along each edge. The curves are named after Jules Antoine Lissajous, who produced them in the 1850s with mirrors glued to tuning forks.
Try this
Move the pointer to set the two frequencies, from 1 to 6 on each axis.
