Nyquist noise theorem

The mean square value of the voltage noise produced by a resistor at the frequency v, with Av band, is known as the Nyquist-Johnson theorem [see also our previous paper ]. 

The noise thermometer is based on the temperature dependence of the mean square noise voltage V2 developed in a thermistor (Nyquist theorem, 1928) ... 

The SIN defined by Equation 7.6 for a given NMR resonance is proportional to the square of the nuclear precession frequency (mo, rad/s), the magnitude of the transverse magnetic field (Bi) induced in the RE coil per unit current (/), the number of spins per unit volume (Ns), the sample volume (Vs), and a scaling constant that accounts for magnetic field inhomogeneities. The SIN is inversely proportional to the noise generated in the RE receiver and by the sample (Vnoise) as defined by the Nyquist theorem,... 

It is only a small step from here to the equivalent statement, known as the Nyquist theorem, for current noise of thermal fluctuations in a circuit with resistance R.4... 

Nyquist theorem - An expression for the mean square thermal noise voltage across a resistor, given by RkTAf where R is the resistance, k the Boltzmann constant, T the temperature, and /y the frequency band within which the voltage is measured. 

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