Lightning in Water

[mooeypoo]

I have a question someone asked me in my time in the military, and though I tried researching it, I am not sure I understood it correctly.

 

Lightnings are "drawn" to anything that dissipates their charge - this is how, as i understand it, you can see a lightning hit sand (there was an occasion i have seen in Discovery Channel once), transforming the sand in its path to glass, and end up touching an underground metal wire-tunnel.

 

Is it possible for a lightning to hit water?

 

If so, what would happen to a fish (or a person, for that matter) that is near it, and how "far" away would a life form (fish or person) should be to be relatively safe? What would dissipate the Lightning's electrical charge, and why would it be drawn to the surface of the water in the first place and end up hitting it?

 

Thanks for any information!

 

~moo

[Rocket Man]

lightning is caused by a difference is electrostatic charge, the charge in the cloud causes the ground to adopt an opposite charge, this charge is neutralised to an extent by the current in the lightning. (the voltage difference reaches the break-down of air and arcs over, allowing the eletrons to move)

 

lightning can and does hit water

the charge neutralises in all directions into the water because it is the thing with the opposite charge

 

the aspect of electricity that kills people in water is the current density; ampage per square cm. when this gets to a certain limit across the heart, the heart stops.

more area, less current density.

 

when lightning hits water, the water can boil explosively due to the heat the current causes

the curent density will decrease with increased distance from the point the lightning strikes and so, the heat produced will drop off as well

(i think the electricity would kill quicker than the heat)

 

when lightning hits fresh water, there is low conductivity, so any electrolytes will carry the current more effectively due to the decreased resistance. so any fish / person in freshwater is going to carry more current than the water.

 

however, when it hits seawater, the salt in solution has a lower resistance than the electrolytes in blood, you'll have a current shunt around your body, and cop less current than if you're in freshwater.

 

so basically, the killing distance is determined by the bolt itself, and the conductivity of the water. fish dont die because they have less conductivity than the surrounding seawater.

[mooeypoo]

So if I understood you correctly, freshwater fish WILL be fried if that happens?

 

I'm.. trying to get my mind to unboggle. hehe Lightning's always been something hard for me to grasp..

 

~moo

[reor]

Fish can sense electrical charges and hide on the ground when there's a lightning about to charge up.

[Rocket Man]

So if I understood you correctly' date=' freshwater fish WILL be fried if that happens?

 

I'm.. trying to get my mind to unboggle. hehe Lightning's always been something hard for me to grasp..

 

~moo[/quote']

 

 

think this way, you're passing a current away from a point, the curent has trouble going through the medium it is forced to go through, so it will take any opportunity to pass through anything more conductive to get away.

in the case of freshwater fish, the fish are probably more conductive than the surrounding water so they will have a higher current density, higher current density means more ohmic heating and more neural/physiological damage.

 

in seawater, the current will avoid fish/people because they have a higher resistance(in some cases) so the current density through the fish will be lower at the same distance because it is shunted by the water.

 

reor, good of you to raise that point, most fish can detect the charge in the water just like when you feel electrical storm gathering or a vandegraaf generator turned on.

also, freshwater is often shallower than seawater, so the current is more likely to go straight down into the more conductive soil. so you're left with less lethal area.

[woelen]

I have a question someone asked me in my time in the military' date=' and though I tried researching it, I am not sure I understood it correctly.

 

Lightnings are "drawn" to anything that dissipates their charge - this is how, as i understand it, you can see a lightning hit sand (there was an occasion i have seen in Discovery Channel once), transforming the sand in its path to glass, and end up touching an underground metal wire-tunnel.

 

Is it possible for a lightning to hit water?

 

If so, what would happen to a fish (or a person, for that matter) that is near it, and how "far" away would a life form (fish or person) should be to be relatively safe? What would dissipate the Lightning's electrical charge, and why would it be drawn to the surface of the water in the first place and end up hitting it?

 

Thanks for any information!

 

~moo[/quote']

Definitely lightning can hit water and the effect of the lightning depends on the amount of salt-like compounds dissolved in the water. In fact, I have done an experiment with high voltage capacitor discharges in water. The effect is quite stunning and from the point, where the spark hits the water, new paths of conduction are created, along the surface of the water.

 

Inside the water itself, a potential gradient is formed. At points, where there is sufficient conductivity, channels of ionisation are formed and we perceive these as new sparks (lightning bolts, when on a large scale).

 

With my experiments I indeed have had explosions, with water being sprayed around extremely violently, such that the water droplets, hitting the skin, really hurt (merely by their impact velocity, not by heat or electrical charge).

 

Have a look at the thread I created in the chem section:

 

http://www.scienceforums.net/forums/showthread.php?t=21864

 

Originally I wanted to do simple electrolysis, but at the end of the experiment I obtained big loud bolts of lightning, with star-shaped sparks along the water-surface. Go to the end of the page for the pictures. Especially the sparks, moving along the surface, are quite spectacular.

[Mokele]

Actual lightning strikes have variable effects, as noted earlier. As for fish, I know that in freshwater at least you can capture fish using electricity. Low currents stun them temporarily, high currents permanently damage or kill them. The technique of electrofishing with low currents is often used for non-destructive sampling of river ecosystems.

 

Mokele