Several problems in quantum optics in which spontaneous emission or vacuum fluctuations play can be found and discussed. However there are some classical examples and also some non physical cases can be found which are quite analogues to zero point fluctuation or vacuum fluctuation. In the present work we investigate such cases for the sake of analogy only. Examples are triode oscillator, tetrode oscillators, heartbeat; build up of longitudinal growth of biological samples. Another example is the growth of dimensionless intensity in a Laser cavity. We have discussed about fifty such cases where fluctuations are involved. It may however be noted that the vacuum fluctuation is the outcome of a fully quantized theory of radiation. And there is no actual analogy that exists in classical or semi-classical field.
