How much water could the average lightning bolt vaporize?

Question

Optional embeded second question, Why doesent the lightning rod melt?

Answer 1

Not very much, but it depends on the particular lightning bolt. Some--we don't know how many--carry enormous currents for long periods. What you have to know is the actual energy imparted by the strike on the load--that is, your water. That particular figure is a bit tricky to come by, but it's lower than you might think: the resistors used in some lightning laboratories for wave-shaping purposes are merely plastic tubes filled with salty water, and they only get hot under unusual circumstances. (When that happens, they squirt salt water all over the equipment, which is no fun to clean up and the lab director becomes upset, too.)

Most strokes do not carry current for long enough to melt anything: currents range to thousands of amperes, but only for a few microseconds. The standard IEEE lightning waveform rises to its maximum voltage (perhaps a couple of million volts, usually less) in 1.2 microseconds and then drops to half of its previous voltage every fifty microseconds thereafter.

Lightning rods _can_ melt, but because most lightning strokes last for such a short period, the high currents don't flow for long enough to make things even warm. In an artificial lightning laboratory, we used very thin wire--20-gauge tinned hookup wire, without insulation--to make connections from Marx generator to wave-shaping network to whatever device we were testing.

Note that this implies a belief that many objects which are struck by natural lightning show no damage, and it turns out that this is indeed the case. It makes research in the field of lightning damage amazingly difficult; things can be struck, but without a witness or instrumentation there's no way to tell if a strike actually took place.

Answer 2

2. The lightning rod does melt some times. When it does not the electrical force is conducted through it via the ground so rapidly that it does not get hot enough to melt.
1. There is the theory and the practice. In theory the billion (10^9) Joules in a lightning bolt would vaporize a lot of water, but since it happens in such a tiny fraction of a second, the water would be converted to a plasma and blast the rest of the water apart - just it does to the wet air, we hear the blast as thunder. Since "latent heat of evaporation 2.27 MJ/kg ", roughly 1,000 KG of water could be vaporized (boiled) by the energy, which is a tonne (about 2200 pounds) of water if it could all be gotten into the water.

Answer 3

The average lightning bolt contains 10^9 - 10^10 joules of energy - say average number is 5.5x 10^10 Joules.

I takes 2.23 x 10^6 Joules to vapourise 1 kg of water.

1 lightning bolt could vapourise 5.5x 10^10 / 2.23 x 10^6 kg of water = 24,664 kg of water - say approxiamtely 24.7 tonne of water.

In reality this does not happen, for the same reason taht the lightning rod does not melt. A lot of the energy from the lightning bolt is dissipated as heat (warming up the surrounding atmosphere and area) and as noise (thunder).