ELECTRIC DISCHARGE PHENOMENON

The flow of electricity through metallic solids, or through liquid metals is called Conduction.

The electricity  flow through ionic solutions (such as NaCI) gives rise to the phenomenon called Electrolysis

The flow of electricity through gas (ionised) is called as "Electric Discharge".

There are many types of electric discharges. For example, there is an electric discharge that is taking place inside a fluorescent tube, neon signs, etc.

If we connect the resistor (R) to a power source of voltage (V) then the current (I) drawn by the resistance will be equal to I = V/R. (Ohm's Law).

Since, the cross section is uniform, the resistance per unit length is also uniform. Hence potential distribution along the length is linearly sloping down from V at the end connected to positive and comes down to zero at the end connected to negative. Similarly, we can find out the potential distribution along the arc column. We know that it will be difficult to measure the potential distribution along the arc column, because of the very high temperatures (about 3000 to 10000 ° C). We will require special probes to withstand the temperatures and some special equipments and methods. Nevertheless scientists have done this work and they have found out a surprising result.

The potential drops heavily near the anode and cathode. The regions over which there is a large voltage drop near the anode and cathode are called anode region and cathode region respectively. It is also surprising to note that the length of anode and cathode regions are very small of order of 0.01 mm and less. Since, the same current is flowing across the arc, the power that is developed near the  anode and cathode are considerably  higher, as the voltage drop near the anode and cathode are high.

                P_a = V_a X I(power at Anode)
                P_K = V_K X I(power at Cathode)

                V_a= Anode drop
                V_K = Cathode drop

The power or heat is responsible for the heating and subsequent melting of the electrodes.