Long description
This is a screenshot from Interactive 3, showing just the bottom wave. As usual, the horizontal axis shows time from 0 to 20 milliseconds and the vertical axis shows voltage from minus 1 to 1 volt. There are 8 oscillations of a ‘rectangular’ shaped wave in which the ‘flat’ tops and bottoms of the wave have small ripples corresponding to the high-frequency components. The vertical sides of the rectangles slope left to right a bit as they go down from 0.6 volts to minus 0.6 volts, and slope the other way as the graph rises from minus 0.6 volts to 0.6 volts. This is quite a convincing approximation to a rectangular wave.