Electric current in gases

For metallic conductors and electrolytes, the dependence of the current strength on the voltage is linear, ie, the current in such conductors increases in proportion to the voltage. The laws of conductivity in gases are much more complicated. Consider an electric current in gases flowing under the action of an external ionizer.

Let us turn to experience. We take a capacitor and charge it, creating a voltage between its plates. The electrometer connected to the plates of the capacitor always shows the same voltage: therefore, air under usual conditions is an insulator, that is, it does not contain free charged particles.

Bring a lighted spirit lamp or match into the area between the two plates of the condenser. We note that the voltage existing between them decreases, the capacitor is discharged, hence an electric current arises between the plates. All this indicates that in the air between the plates under the influence of the flame appeared charged particles. What are they?

It is quite natural to assume that such charged particles are air molecules which, under the influence of a flame, received electric charges and, turning into ions, began to move in the electric field between the plates, creating an electric current in gases, which led to a decrease in the voltage on the plates of the capacitor.

Through careful studies it was found that the carriers of electrical charges in gases are ions and electrons that arise in the gas as a result of the action of an ionizer on it.

Ionizers are flames, X-rays, rays emitted by radioactive substances. Any ionizer, whatever its origin, has the ability to create in a given volume for a certain time a certain number of positive and negative ions.

Under the action of the ionizer, the gas molecules lose electrons and become positively charged ions. The liberated electrons, first, themselves become carriers of electric charges, and secondly, joining neutral molecules or atoms, form ions that are negatively charged. In this way, free charges can appear in the gas in the form of electrons and ions of both signs, that is, an electric current appears in the gases.

The charged body, being in the ionized gas, attracts to itself free charges of the opposite sign, which both neutralize the charges on the body, as a result of which it is discharged.

The gases do not separate their constituent parts on the electrodes, as is the case in electrolytes, since during the ionization of the gas the molecules do not decay; They only lose or add electrons to themselves.

Gas ions, coming to the electrode, give it their charges, turning into neutral molecules or atoms, and diffuse back into the gas. In electrolytes, the ions that approach the electrodes either deposit on the surfaces of the electrodes, or enter into chemical reactions.

If the ions and free electrons formed in the gas are in an electric field, then they acquire directed motion. It follows that the total electric current in gases is two streams of charged particles, one of which goes to the anode, and the other to the cathode. It is accompanied by a number of unique phenomena. These include the various types of glow of gas in the discharge - from a weak, hardly noticeable glow of high voltage wires to the dazzling bright light of the electric arc and grandiose flashes of lightning. Electric current in media (solid conductors, electrolytes) does not cause such phenomena.

Finally, under a gas discharge, it is possible to observe specific chemical reactions that do not occur under normal conditions: the formation of oxides of nitrogen and cyan in air, the formation of molecules in monatomic gases, and others.