Quote:
Originally Posted by mark christopher
im struggling to see how that works in bold.
water is an insulator  out of curiosity, what water did you use? |
No prob, I can try to explain.
Electrical current is the movement of charge carriers through something. E.g. electrons moving through copper wire.
In metals, there are lots and lots of electrons floating around that are not tied to any particular atoms - they can easily move from atom to atom within the piece of metal. They are all negatively charged. If a pair of positive and negative electrodes are touched to the metal - these electrons are attracted to the positive electrode. And when they move - current flows!
In pure (or even pretty pure water like tap water) there are very few charge carriers around. Unlike metals, where there are millions of atoms all put together in a big mass sharing each other's electrons, water forms molecules. Each molecule is a "bundle" of 1 oxygen and 2 hydrogen atoms. This tightly-bound bundle has the same number of negatively-charged electrons and positively-charged protons in total in it - so it's neutrally charged. The molecule "could care less" if there were electrodes inserted into the water, as it wouldn't be drawn to either of the two. Hence, current does not flow.
In _salty_ water, there's are lots of charged ions floating around as well as water molecules (e.g. Na+ and Cl- if you dissolved table salt into water). These ions can also be attracted to their oppositely charged electrodes and move - causing current.
Of course this is a bit of a simplification, but basically water is a pretty good insulator at normal voltages. Sea water, no. Muddy water, no. But fresh water or tap water, yes.
As you know, you can even run a brushed motor no problem underwater, power leads and all!
Ok, I'll get off the soap box now... still doesn't change the fact that my switch is melted into goo!
Cheers,
Ty