CRT Oscilloscope

1. Thermionic emission. A filament heats the cathode to approximately 1000 °C, enabling electrons to escape from its surface into the vacuum. The orange region at the rear represents the heated cathode assembly.
2. Control grid. A negative electrode near the cathode regulates beam current. A more negative grid voltage reduces current and therefore lowers trace intensity; this is represented by the Intensity control.
3. Electron gun. Anodes at approximately +2 kV accelerate electrons to about 9% of the speed of light in the nonrelativistic approximation. The focusing electrodes act as an electrostatic lens and control spot size.
4. Vertical deflection. The input signal is applied to plate pair ④. In the idealized uniform field, the beam follows a parabolic segment between the plates and a straight path afterward. Within the modeled operating range, screen displacement is approximately proportional to instantaneous plate voltage.
5. Horizontal sweep. A sawtooth voltage moves the spot from left to right at approximately constant speed, then returns it during a blanked flyback interval. Trigger sync begins each sweep at a rising zero crossing so repeated traces remain aligned; disabling it allows phase drift.
6. Phosphor screen. The phosphor emits visible light where the electron beam strikes. Finite persistence causes recently excited points to decay gradually, producing the displayed fading trace.

Time scale: at the modeled accelerating voltage and tube dimensions, an electron transit is on the order of 10 nanoseconds. The exhibit therefore treats the beam position as responding instantaneously relative to its displayed low-frequency signals.

Try: X–Y mode for Lissajous figures (set 2:3 and adjust phase) · defocus the lens · reduce intensity to zero · disable triggering · reduce persistence.