Why does electric discharge occur?
I understand how it happens. The charges in the cloud get separated due to winds, the negative charges move down, while the positive move up in the cloud. The negative charges then starts to repel the negative charges at the ground causing the ground to become net positively charges. Then something called a ''ladder'' happens. The negative charges of the cloud starts moving down looking for positive charges, while the positive of the ground move up to find negative. When they meet, the discharge occurs.
That's all fine, just one question - WHY?
Why do the negative and positive charges need to ''find'' each other, and move towards each other aka discharge? So the negative charges need to do what? Move to find the positive, and then what happens? both disappear? The cloud was net neutral i.e. both negative and positive charges were present, so why when they get separated, they need to ''collide'' with each other? why did they not do that while they were neutral in the first place?
- Andrew SmithLv 79 months ago
Electron affinity is different for different materials.
This is identical to charging a rod by rubbing it.
The electrons move a small distance to a more attractive material.
If the material is NOT MOVED then everything is in balance.
But we now MOVE the material. Separating the charges by a greater distance and in doing so add energy.
Not only have we added energy but this causes an electric field.
The charges attempt to get back to their equilibrium position releasing energy.
Now to the cloud. From your description the air, next to the cloud, gains some electrons from the cloud.
Now the air is moved away taking the charges with it. Note that this works best with dry air.
When it is some distance away there is no longer any great force from the cloud and the charges spread out. Some of them enter the earth making the earth somewhat more negative and leaving the cloud positive.
Eventually so much charge has built up on the cloud that the electric field reaches the breakdown voltage of the air ( ionization field). This can be from 100kV per metre up to perhaps 1 million volts per metre.
All it takes now is some irregularity in a surface which locally has a higher electric field.
That starts to ionize first. But this reduces the distance to the cloud which increases the field.
So a bit more of the air ionizes. And so on.
Once it is all ionized then the path is fully conductive and a high current flows.
Discharging some of the electricity from the cloud.
Basically it is the addition of energy through the motion of insulating bodies that powers the whole system.
Incidentally as this takes energy from the wind that would mean that the wind speeds would be higher without this effect. Interesting.