How does one see the effect of a single electron?

Now the supply voltage is doubled from 240V to 480V. The voltage between each dynode is therefore doubled as well. A photon struck the photocathode of the photomultiplier tube to the left, and an electron is being accelerated to the first dynode. How many electrons will be ejected by the first dynode?

Since the voltage between the photocathode and the first dynode is 160V, four secondary electrons are emitted. In the previous example, the voltage between the photocathode and first dynode was 80V, and two secondary electrons were emitted. After one stage, doubling the voltage also doubled the number of secondary electrons. How many electrons will there be after the second stage?