Question

Lightening occurs due to the movement of the charges from the clouds to the earth......But charges can move only in a conducting medium( like copper wire, electrolyte etc)....but for lightening the atmosphere (which is an insulator) is the medium......how do charges move in a insulating medium???

Answer 1

When the voltage between the cloud and the Earth becomes large enough the air becomes a conductor. This means that instead of just having neutral atoms and molecules the air has many charged particles in it (ions and electrons) and it is these mobile charge carriers which are responsible for the electric conduction process.

The process of by which lightning occurs is very complex and it is very often the case that there is a "leader" before the main discharge which travels from the cloud to the Earth which forms the conducting path. It is very faint and so is not often seen.

Here is a video of one and you can see many more by Googling something like "lightning leader"

https://www.youtube.com/watch?v=GTo2u8gNL0Y

Answer 2

have you heard of action of points??
if you have a very pointy conductor, charges will leak off of it?

Answer 3

ya.....why does it happen??

Answer 4

@Mashy Why does electric discharge take place at pointed ends?

Answer 5

they say its CORONA DISCHARGE

Answer 6

If the electric field exceeds about 3 million volts per metre the are becomes a conductor.
For a given amount of charge on a conductor the electric field at the surface of the conductor depends on the (radius of curvature) of the conductor.
If the radius decreases, the curvature increases, the electric field increase and so there is more chance of the air becoming a conductor.
A pointed lightning conductor not only is there to direct a lightning strike towards itself and so save a building it is also there to help discharge the cloud in a less violent way and thus reduce the probability of a lightning strike..

Answer 7

why does electric field depend on radius of curvature? @Farcher

Answer 8

from wikipedia -"If a charged object has a sharp point, the electric field strength around that point will be much higher than elsewhere" -----this is all i want to know ....

Answer 9

WHY?

Answer 10

If you have a strong field, lets say a strong positive field.. then the electrons of the air molecules will get pulled towards the field, and the nuclues away from the field, so that starts INDUCING dipoles.. right?
now suppose one of the atoms get ionized, (it can happen due to many reasons, dont worry how ) so then the electron will accelerate like crazy and may ionize something else.. and this becomes a run away effect.. and so now what is happening is the field is basically producing ions
the electrons will satsify the positive charge of the conducor.. so you see how this works eh?

Answer 11

E = kq/R^2
if r is small.. E is high :P