2
$\begingroup$

A capacitor in parallel with a resistor will have a random noise $\mathrm{voltage^2}$ across it of average value $V^2 = k_{B}T/C$. If this is a parallel plate capacitor, you can show that the average attractive force between the plates is $k_{B}T/d$ where '$d$' is the spacing.

Note that this is not the same as the Casimir Effect (which is a quantum effect) -- it is a consequence of the thermal variation in the charges on the plates.

Is this effect significant in the universe between bodies ? Does it have a name ? Is there any practical use or effect ?

$\endgroup$
1
$\begingroup$

One could easily estimate the magnitude of this force for a typical capacitor at room temperature - as expected, it is a very small force that can be neglected.

I am not aware of any special name for this effect, but thermal fluctuations. In the context of light bulbs (which are very similar to capacitors) we also speak about thermal emission from the cathode - the thermal fluctuations make electrons leave the cathode, and then they become accelerated towards the anode by the applied bias.

The important difference between thermal fluctuations/noise and the effects like the Casimir effect is that the one can nowadays conduct experiments at extremely low temperatures (micro-Kelvins temperatures are somewhat of a routine) where the thermal effects become smaller and smaller, unlike the quantum effects.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.