# Naked Science Forum

## Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Petrochemicals on 29/12/2019 16:32:48

Title: How much energy is in a bolt of lightning ?
Post by: Petrochemicals on 29/12/2019 16:32:48
I couldnt find a thread about it so i started a new one.

There are lots and lots of articles on line that calculate the electrical charge of lightning, wikipedia states upto 1giga joule is possible. This seems like alot until you realise that  it is only about 277kwh, or 90 kettles boiling. BUT this is the electrical charge, what about the other energies used or released. Lightning would not occour if there where too much resistance to overcome.

Lightning  plasma tunneling is stated to be an easy way for lightning to create a bridge through the air and span the distance. But what of the light and  noise released to begin with. An average lighning strike at one mile is very very easily heard and seen, they say count to 7 and its a mile between flash and sound (that would be  4000m or 2.5 mile?).  Thats a radius of a mile of vibrating air and bright light. Then there is the heat that the lightning creates, hotter than the surface if the sun.
Title: Re: How much energy is in a bolt of lightning ?
Post by: alancalverd on 29/12/2019 17:45:46
All the effects are derived from the  electrical energy.

277 kWh is the energy required to bring 3000 kettles to the boil.
Title: Re: How much energy is in a bolt of lightning ?
Post by: Petrochemicals on 29/12/2019 18:59:18
All the effects are derived from the  electrical energy.

277 kWh is the energy required to bring 3000 kettles to the boil.
90 ketttles boiling for 1 hour. I would say well corrected, but 3000 kettles is not alot really.
Title: Re: How much energy is in a bolt of lightning ?
Post by: evan_au on 29/12/2019 19:51:44
Quote from: OP
How much energy is in a bolt of lightning ?
The current of a typical "negative" lightning bolt is often quoted at around 10-20kA.

The breakdown voltage of air is around 0.7 MV/m (damp) to 1 MV/m (dry).
- If the cloud is 1km above the land, that could reach an impressive 1GigaVolt.

Normally, you would calculate Power = Volts x Amps = 104A x 109V = 1013W
- But the voltage is present before the air reaches its breakdown voltage (when the current is almost zero)
- And the current is present after the air reaches its breakdown voltage (when the voltage across the ionized is relatively low)
- So the power is not as high as you might expect

Energy can be calculated as Energy = Average Power x Time
- A common model for testing lightning surges in electrical circuits typically has a rise time of 6us, and a fall time of 20us, so the duration is quite short, of order 10-5 seconds, so the energy is not as high as you might expect..

But lightning voltages, currents and energy is high enough that it will destroy any electrical circuit it contacts directly. So the usual strategy is to provide a high point that will attract the lightning, and a straight-line, low-inductance/low resistance path to earth that will divert the current around any electrical circuits or other valuables (like your house).

"Positive Lightning", though much rarer, has higher voltages and currents.
See: https://en.wikipedia.org/wiki/Lightning#Positive_and_negative_lightning