Figure 5 shows a rectifier circuit not unlike figure 3. A transformer has its secondary bottom end connected to common. The other side is connected to the plate of a vacuum diode. The primary is not shown as connected to anything but it is assumed that it is connected to a source of AC. The filament of the tube is powered by a battery. The side of the filament which connects to the battery positive also connects to a resistor. The other end of the resistor goes to common. There two voltmeters in the circuit. One is connected from the plate of the diode to common and the other is connected across the load resistor. Both meters have zero marked at the center with positive voltage to the right and negative voltage to the left. These unreal meters can follow individual cycles of the input AC. As the animation runs the pointer of the meter on the plate of the tube moves slowly to the right and returns to zero continuing on to the negative extreme and returning to zero again. This keeps repeating. The meter across the load resistor indicates the same voltage as on the plate when that meter is positive only. When the meter on the plate goes negative the one across the load resistor remains at zero. In the tube small dots represent electrons. When both meters are positive the electrons come out of the filament and are absorbed by the plate. When the plate meter is negative the electrons come out of the filament go about half way to the plate then turn around and go back to the filament where they are reabsorbed.