10 May 2012

Making revision 'fun' part 3: Static Electricity - Sparks = 'splosions

 So, this is another one of those revision posts I meant to do a lot more of. I don't think you missed much, but whatever. This one covers the stuff in GCSE Physics/Additional Science (I'm doing Physics, but the content should be the same (as of 2011-12)) about static electricity. As with my Geography post about the drought (and the rain, and why the drought is still a thing), there are a metric ton of caveats regarding my personal knowledge. That aside, let's get this thing started.

Static electricity, as the name would imply, is basically a build up of charge which is pretty still (I.e. isn't being conducted throughout the charged object), and we generally experience it through either making our hair stand on end for shits and giggles* or those annoying electric shocks. This build up of charge comes through a transfer of electrons. If the charged object gains electrons, it gains negative charge. If an object loses electrons, it gains positive charge. Polythene's an example of the former, acetate the latter. Fairly simple, right? Well, yeah, it is. That is, assuming the standard of 'lies (well, simplifications) to teenagers' which typically comes into play in these situations doesn't actually apply here. I'll know for certain in a year or 2 when I'm done with my A-levels.

Generally speaking, the transfer of electrons comes from friction - for instance when walking across a carpet or taking a jumper off or rubbing a balloon against a curtain/person's hair.

Of course, the hair standing up on end thing is caused by like charges repelling and unlike charges attracting, which is due to some stuff which I'm going to have to explain using personification. To wit, the positively charged object wants more electrons, whilst the negatively charged object wants to lose electrons. Also, electrons don't like each other for some reason (since they're all negatively charged, so repel each other).

The attraction created by static electricity has uses other than shenanigans (for a given value of 'shenanigans', of course. The attraction has uses in stuff like printers, photocopiers, those smoke scrubber chimney things and spray-painting cars. I'll use those last 2 as an example, since I know them off the top of my head and they strike me as most likely to come up in the exam.

The SSCTs consist of two either earthed (connected to ground) or positively charged collection plates up the side of the chimney, with a negatively charged grid in the middle of said chimney. Smoke particles in the, er, smoke float up through the grid, gain negative charge, and then get attracted to/stuck to the collection plates, for later scrubbing off. This means less smoke particles get into the air proper, which is cool, I guess.

The car thing is even simpler -  the body of the car is given negative charge, whilst the friction of paint droplets being forced through the narrow funnel of the paint sprayer gives them positive charge. This makes them stick onto the body of the car at least for long enough for them to be made to stick permanently.

Right, now to get to the explosion stuff. I mentioned earlier about those annoying little electric shocks, well, that's a spark. There are quite a few environments where sparks are a bit of an issue, probably the most obvious one being petrol stations - where there's loads of highly flammable gas floating around. More obscurely, surgeons apparently have to be earthed with a wire lest (the also highly flammable) anaesthetic gases catch light due to a spark. Sparks, in situations like these, equal explosions (or "'splosions" if I'm in the mood for forced alliteration). Obviously, a hospital is probably the very last place anyone wants an explosion, so preventing the static build up using the aforementioned earthing techniques is kind of important.

Not all of the undesirable effects of static are as explosiony though - if you're fixing a computer (which I've never done) you also need to prevent static since it can damage the delicate internal circuitry of them (or something like that).

Okay, that concludes this (probably incoherent) amble about a random topic that one of my GCSEs covers. Come back if/when there's a next time and see what dumb idea I decide to do then!

*sorry for the crudeness - I really couldn't come up with a funnier way of phrasing this.

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