I recently saw a question posted on LinkedIn about whether purely reactive components produce noise like resistors do. This, of course, would be Johnson Noise, also known as Thermal Noise. I do not recall any mention of such noise in reactive components (inductors and capacitors) in my studies, other than the that attributed to the resistances associated with these components. And there is not much written about this subject. The few times I have seen anything written about this, it is stated that reactive components do not have Johnson Noise. I suppose this is true in that Johnson Noise is defined as the familiar square root of 4kTRB, where k is Boltzmann’s constant in joules per kelvin, T is the resistor’s absolute temperature in kelvin and R is the resistor value in Ohms. There is no L or C in this formula and pure reactances have no resistance.

 

But, is there is any noise at all associated with pure reactances?

 

My thought is that there probably is some noise associated with reactive components, although I can not prove this. My thought is that this noise is rather small and results from quantum effects. Quantum mechanics deals with and quantum effects results from what happens on a nano scale.

 

It seems to me that electrons probably do not pass from one atom to another smoothly, but jump from one atom to another. This results in a very small energy spike or pulse. When many electrons pass (or rather, they jump) from many atoms to many other atoms, a small amount of deviation from the “normal” waveform is probably happening. This deviation would be noise.

 

The amount of noise thus produced would necessarily be very small. If it were large it would have been noticed and some study or research would have been done to determine the cause of this noise. If the noise is small enough by comparison with any other circuit noise, it might go completely unnoticed. Since the flow of electricity involves literally millions of electrons, the average amount of noise produced by quantum effects is more than likely nearly zero, so might be difficult to detect, especially if it was not being looked for. I would think that a search for this noise and the levels at which it may exist would have to start from a theoretical and mathematical viewpoint to determine whether such noise might exist and at what levels it might exist, but that is beyond my abilities and interest, even though I find the very question of reactive noise a very interesting one. Perhaps a Quantum Researcher or PhD candidate might find researching this to be an interesting challenge.