An experimental arrangement used for measuring the distribution of molecular speeds is shown below in the Figure 4.1. (a) Briefly explain how the apparatus operates. [4] (b) Describe the observed distribution of molecules that appear on the screen. [6] Figure 4.1 4.2 In a metal, the valence electrons are not very strongly bound to individual atoms, and consequently travel rather freely throughout the volume of the metal. By treating these electrons as a "gas" that obeys the Fermi-Dirac distribution, show that the mean energy of the electrons is 3 5 th of the Fermi energy.