A Neon tube consists of two electrodes with a potential diff

A Neon tube consists of two electrodes with a potential difference between them. As a result of collisions with themselves and with the electrodes the neon atoms in the tube are ionized. The electrons are accelerated towards the positive electrode and the positive ions towards the negative electrode. A discharge like that in lightning (i.e. a high current generated by avalanche ionization) is prevented by inserting a resistance in series with the lamp (which reduces the potential across the lamp when the current increases). The generated electrons are thus capable of exciting the atoms but not ionizing them. Estimate the density of atoms and the pressure of the gas inside the lamp if it works on 110V (assume that the length of the tube is 1m and that the lamp emits red light, with energy ~ 2 eV)   

Solution

density of atoms = 110/2 eV = 55/ 1.6 x 10^-19 = 34.375 x 10¹⁹ atoms/m