In the late 1700s, Charles Augustin Coulomb put the snap, crackle and pop from a number of perilous experiments together and deduced the form of the electrostatic force law. Here’s what he found:
- You can’t tell just by looking at an object whether or not it carries a charge. Unless you’re an X-Man. Possibly.
- There are only two types of charge: positive and negative. Opposites attract, as the old cliché goes. And an object with equal amounts of each is electrically neutral, like Switzerland.
- All normal matter contains electric charge (except Findus lasagnes, which are not yet understood by science).Electrons may be transferred from one object to another.
- In an isolated system, the total electric charge is always conserved. So when you rub a balloon on a cat, no charge is created – electrons are simply redistributed between the cat and the balloon (and anger is created in the cat. Cats are often not subject to the usual laws of physics. Mine can teleport). Charge has its very own law of conservation.
- Because of the attraction between unlike charges, any item with a deficit of electrons (which has, therefore, a positive charge) will attract negatively charged items. But that’s not all: it will also pull in any electrons that happen to be hanging around. That’s how electric currents work, in the very simplest terms. Put a negative thing next to a positive thing, and electrons will flow from one to the other until they’re sharing them equally.
Fun facts about electric charge
Me. On a Monday.
If you super-dry your hair then give it a vigorous brushing, you can make it stand on end. I often don’t need to put this much effort in; my barnet’s natural state appears to be one resembling those little trolls.
- You can stick balloons to the ceiling using electrons, thus defying the laws of gravity. This is an interesting demonstration of the difference in strength between the electrostatic force and the gravitational force. Relatively speaking, the electrostatic force is MUCH stronger. Mind-bogglingly so. (Although you can’t really compare them, because they are fundamentally different things with arbitrary units of measurement.
- If you’re wearing nylon clothes, and you take them off in a dark room, you can sometimes see sparks as the separation of the clothing from your skin causes the air around you to undergo electrical breakdown. You can dismantle the air, like an X-Man. Possibly.
- Electrostatic charges are responsible for lightning. (More below.)
One of my favourite things is finding out that an everyday (but brilliant) phenomenon is still not fully understood by our biggest brains. We really don’t understand how lightning works! Partly because experiments are bloody dangerous…
A scientist named Georg Wilhelm Richmann, a German physicist living in Russia, was killed during a lightning experiment in 1753. He has the dubious honour of being the first person killed during an experiment involving electricity.
He was electrocuted in St Petersburg while “trying to quantify the response of an insulated rod to a nearby storm”. Any excuse to duck out of a meeting, even back then: he dashed off on hearing the news of a thunderstorm, taking his engraver with him to record the event for posterity.
During the experiment, and somewhat predictably (with the benefit of hindsight), he was struck by lightning. (It’s said that it was ball lightning, a very rare phenomenon that wasn’t believed to exist until the 1960s.)
The explosion that followed blew up his shoes, singed his clothes and knocked him dead. That wasn’t the end of his scientific exploits, however; his body was dissected to find out what effect his terminal experiment had on his organs.
We don’t understand lightning
Lightning is probably the most dramatic and well-known natural phenomenon resulting from electrical charge. But how does it work? Well, here’s what we know:
- On humid days, rising air currents carry water vapour up into the atmosphere.
- This occurs in giant clouds – they’re around 10km thick.
- The water droplets cool as they rise, then freeze to form hailstones. Hailstones are required for lightning to occur.
- The hailstones grow as more water condenses on them, then begin to fall under gravity when they become obese.
- As they fall, they tend to melt and emerge from the cloud as heavy rain.
- Lightning flashes develop near the base of a cloud, and are caused by the separation of positive and negative charges within the cloud.
- The electrical activity occurs at an altitude where the temperature is between 0°C and -10°C – the only temperature range in which both hailstones and supercooled water drops can exist simultaneously.
Beyond these facts, we’re not really sure of anything!
We all know what lightning looks like, but this video shows a whole plethora of beautiful phenomena set to the strains of Robert Miles epic tune ‘Children’. One of the soundtracks to my messy youth.
Theorising about lightning
Most of the theories about the origins of lightning are based on a transfer of charge between the rising water drops and the falling hailstones. This leaves the water drops with a net positive charge and the hailstones with a net negative charge.
With the water drops pulled to the top of the cloud by rising air currents, and the negatively charged hailstones falling under gravity, the result is a net excess positive charge near the top of the cloud and a net negative charge near the bottom.
Diagram illustrating the charge distribution in a thundercloud.
This process increases until the electrostatic charges are so large that one of two things (may) happen:
- The vapour in the cloud undergoes electrical breakdown, allowing the electrons to flow up through the cloud in a giant spark of lightning – a ‘cloud flash’.
- The air beneath the cloud suffers electrical breakdown and the negative charge at the bottom flows to the positively charged ground as forked lightning.
As I said, though, the charging mechanism is not really understood. The middle of a thundercloud is a bit of a hairy place to be, so there are not many experiments documented. I quite fancy making some kind of protective bubble and mooching into a cloud. If anybody would like to fund this hare-brained scheme, do drop me a line. You could be in line to share a Nobel Prize, you never know…