It is a dark and stormy…day. Thunderbolts and lightning, very, very frightening. Mama Mia.
And you are out swimming. OMG! Got to get out of the water and dash for the car.
You are dripping wet as you dash to the car – lightning strikes the Earth everywhere.
As you dash to the car, are you in greater danger from the lightning should you be struck if you have been swimming at the beach (in salt water); swimming in the river (fresh water), or if you are completely dry because you had your towel handy and completely dried yourself before the big dash?
Answer
The short answer is, you are in the greater danger if you have been swimming at the beach and you are wet with salt water.
Salty, fresh, or dry?
Why are we at greater danger if dripping wet with salt water rather than fresh water – or being bone dry?
Electricity is the flow of charge, which can be the flow of electrons or charged particles. Salt water is made up of ions from dissolved salts such as table salt (NaCl). It is these ions (charged particles) that make salt water a good conductor of electricity.
If we use table salt (NaCl) as our salt example dissolved in the water (or ocean) then the ions are the Na+ or Cl-. And now if you add a force in the form of lightning, which is highly negatively charged (powerfully so) and the earth which is by comparison positively charged you have set yourself up as part of a circuit between the lighting and the ground. The ions in the salty water enable a higher current or flow of charge to travel through your body – not good.
Fresh water has only really small amounts of dissolved ions in it and, while it will conduct a current, it is weak compared to salt water.
And what if you are dry there is just the air around you. Air is a poor conductor. Essentially you become a better conductor of electricity from lightning if you are dripping with sea water than if you are wet with fresh water. It is even better for you if you are bone dry.
Check out the experiment below where FLEET’s Professor Kristian Helmerson show how salt water is a better conductor.
There is always a but…
Ah, but for lightning to travels from the clouds to the ground (or across the sky) it has to pass through the air. How does that happen when air is such a poor conductor? It takes an enormous build up of electrons in the cloud to enable the lightning bolt (flow of charge or electrons) to conduct through the air and travel to the earth. But this takes us to another story altogether and for another day. Stay tuned
Prof. Kristian Helmerson has dragged out the concept with the van der Graff machine to give some insight into lightning itself.