if thermal noise exists while no currents in resistor

[alvays]

Hi, all

Will the thermal noise still exists or not?

Alvays

 

[timof]

Will the thermal noise still exists or not?

Yes, thermal noise is present irrespective of the current in or voltage on the resistor.
The thermal noise (power spectral density - i.e. power per Hz of frequency bandwidth) is given by: S=4kTR, so there is no current of voltage entering this formula.

Some other noise mechanisms do depend on current, for example - generation-recombination noise, shot noise, etc.

A more interesting question is - does thermal noise affect the voltage noise on a capacitor?

 

[alvays]

Will the thermal noise still exists or not?

Yes, thermal noise is present irrespective of the current in or voltage on the resistor.
The thermal noise (power spectral density - i.e. power per Hz of frequency bandwidth) is given by: S=4kTR, so there is no current of voltage entering this formula.

Some other noise mechanisms do depend on current, for example - generation-recombination noise, shot noise, etc.

A more interesting question is - does thermal noise affect the voltage noise on a capacitor?

thanks.

I think the answer is yes if there is a resister in parallel with the capacitor. Though the integrated noise over the all bandwidth is determined by kT/C, but the instantaneous one, that is, the random noise should be there any time.

alvays

 

[timof]

A more interesting question is - does thermal noise affect the voltage noise on a capacitor?

thanks.

I think the answer is yes if there is a resister in parallel with the capacitor. Though the integrated noise over the all bandwidth is determined by kT/C, but the instantaneous one, that is, the random noise should be there any time.

alvays

Yes, you are right. The capacitor itself does not generate thermal noise, but it "accumulates" it form resistive components. If you connect a capacitor in parallel with resistor, and then disconnect - there will be a fixed voltage on a capacitor from resistor thermal noise, and for different samples this voltage will be different (random) - with kT/C total noise.