Thermal noise is the noise generated by thermal agitation of electrons in a conductor. The noise power "P" in Watts , is given by "P=KTB". The movement or agitation of atoms in conductors and resistors is somewhat random and determined by the temperature of the conductor or resistor. The random movement of electrons is brought about bythermal agitation of the atoms that tends have increased energy as the temperature rises. This random movement gives rise to electrical voltages within the circuitry known as either, thermal noise, resistor noise, Johnson noise or circuit noise. This noise is existent across the frequency spectrum, meaning the more bandwidth occupied the likelihood of greater exposure.

Example:

K = Boltsmans Constant = 1.3807x10^-23

T = Temperature (Kelvin) = 273K + 20 º C

B = Bandwidth (Hz) = 180x10^3

Noise Power = K x T x B