Johnson noise is the random fluctuation of voltage across a resistor caused by the thermal excitation of electrons within it, and the dissipation of power associated with these fluctuations. In the experiment presented in these pages, an attempt is made to verify the simple temperature-dependence of the Johnson noise power spectrum — the distribution of power over frequency — and to obtain a value for Boltzmann's constant kB along the way.

In What is Johnson noise? we present a simple theoretical discussion of the phenomenon. The model of H. Nyquist predicts a linear relationship between the temperature of a resistor and its power spectrum amplitude; determining the constant of proportion allows one to obtain kB. This forms the main purpose of the experiment we describe, and typical experimental output is summarized in our results. In another page, we detail some of the data analysis required to extract kB. There, we report our final result kB = 1.63(14) x 10-23 J/K and discuss its accuracy.

These pages were written by Leonardo Motta and Benjamin Wilson at Yale University. You may contact the authors at firstname.lastname AT yale DOT edu.


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