CONDUCTION OF ELECTRICITY IN GASES
Electricity can pass through different media. In the case of gases, the atoms or molecules are not packed and they are free to move. In fact, if we confine a gas in a container, the molecules of the gas move in a free random fashion. Because of the absence of charge carriers, unless we produce some charge carriers in the gas, it cannot conduct electricity. If the electrons (negatively charged particles) are made to come out of the binding of atoms, that is, if they are made free, than electricity. The process of freeing the electrons from the atoms is called "ionisation" of gas, because in this process not only electrons but also positively charged atoms are produced. The electron is bound to the atom. Therefore to "free" the electron we have to supply energy to the electron. The energy which is supplied to the atom to remove the electron from the atom is called as the ionisation energy. The unit of energy for ionisation is called electron volts (eV) and it is equal to 1.62 x 10-19 Joules. Different molecules and atoms require different levels of ionisation energy or ionisation potentials.Table below gives the ionisation potentials of different gases.When we ionise the gas, the gas becomes conductive because now the charge carriers are available. If we now apply a potential in the ionised medium, the charges will start to move and we will have current flowing through the ionised medium. The ions which have positive charge will move towards the cathode (-) andthe electrons will move towards the anode (+).