In practice one calculates the noise figure of an electron device by the Rack‐Llewellyn‐Peterson method. In this method one uses the fluctuations in current and velocity at the entrance plane as the input quantities. In a procedure such as the above, one needs to know the correlation between the velocity and current fluctuations at the entrance plane. It is shown in this paper that such a correlation between the above fluctuations is zero under certain conditions.