Key points are not available for this paper at this time.
The Johnson–Nyquist formula for spontaneous voltage fluctuations across a conductor is rederived for metals at a tutorial level within the framework of the free-electron approximation. The spontaneous current fluctuations are linked directly to the occupancy fluctuations in the Fermi–Dirac distribution function for the conduction electrons and to the electron-scattering processes that are responsible for the electrical resistivity. It is also shown that an externally applied Ohmic current through a metal does not affect its thermal noise. The quantum limit of thermal noise is discussed briefly.
Dekker et al. (Mon,) studied this question.