The Oscilloscope

Long a standard tool in the electronics shop, the versatile oscilloscope uses an electron beam to trace the voltage as a function of time. While that is the standard application, a second voltage can be applied to the horizontal deflection plates instead of the timing ramp voltage to produce an xy plot.

Electrons released by thermionic emission from the hot filament in the electron gun are accelerated by a high voltage and focused to produce an energetic electron beam. The phosphor glows at the point of impact of the electron beam, and that glow is persistent enough for you to be able to see the entire trace of the electron beam across the screen.