HERE IS A DIAGRAM IN AN ATTEMPT TO CLARIFY


You can see that the blue wave (electric field) moves up and down across the centre line. If you measured the electric field at any one point it would be +ve or -ve (or zero, mebbe). But the is continually varying, and you have to think that +ve and -ve actually mean in this case, so this is where you're heads will probably explode...

That diagram actually only shows plane polarised light, you can also have the E/B field vectors actually rotate at some predefined rate (circularly/elliptical polarisation), in which case "polarity" of the wave means NOTHING. In the plane polarised case the +ve/-ve direction depend entirely on the particles that emitted them, and there may not be a clearly definition axis in this case anyway.

Really what you need to look at is that when the wave is pointing in a given direction, it will exert a force on a 'polar' molecule (i.e. one with a +/- direction bias) and when it oscillates back to the opposite direction the molecule will go in the oppposite direction - essentially the molecule vibrates with the frequency of the microwaves.

Most "light" is plane polarised.

In regards to the ionising radiation, this is simply what radiation is able to ionise a given atom. To do this it needs to knock an electron out of its shell in the atom, so for a given element there's a set amount of energy needed to do this. Low UV is just about enough to do this in some atoms, but it can't penetrate, which is why we get sunburnt.

Visible light doesn't have enough energy to do this, nor do anything below that (IR, Microwaves/Radio (there's not functional difference between a radio/microwave or really IR/micro, it's just a definition - RADar actually uses microwave frequencies)). If microwaves were enough to cause ionisation and hence cancer, we'd be fucked as visible light would be much worse.

Any other questions?

Oh, I was going to do a quick explanation of sources (I am about to do this in class :D)

 

Radio - caused by large oscillation of electric charges - any A.C. running along a wire 10+cm long will give out a bit of radio wave

 

Microwave - same cause as radio, but shorter wavelength. I always use a microwave oven as a baseline. There's about 2-3 waves fitting into an oven.

 

IR - Now we get a bit smaller, thermal infrared is caused by oscillation of molecules - anything warm (above absolute zero) will be giving off IR

 

Visible - (as well as Near-IR) is caused by atomic vibrations or high energy heating (bulbs, THE SUN)

 

UV - now we start getting into energy transitions in the atom - things getting hit by other EM radiation can cause this and make stuff give off UV. Interestingly, UV paint/ink doesn't "glow" in UV, it absorbs UV light and re-emits in in a lower frequency, otherwise we wouldn't be able to see it.

 

X-Rays - you can give off x-rays with REALLY hot stuff. In fact, old X-ray sources would be similar to a souped up CRT. Also, pulling sellotape fast off the rolls gives off a few x-rays :)

 

Gamma - can only be cause by stuff going on in the nucleus - radioactive materials, nuclear bombs, fission, fusion, or nuclei that have been excited someway.

That's fair enough. I guess it's just not for me.

 

I need two hands to count the number of computers I own and make use of. I use at least 4 of those on a day to day basis.

The polarisation of light or other electro-magnetic waves refers to the plane of vibration; non-polarised light can oscillate in all directions - if it goes through a polarising filter (which is like a grid) then only light in the plane of the grid gaps gets through.

"ing", then.

That wasn't nearly condescending enough to be Sheldon.

Perhaps it is somebody masquerading as him! Shocking if so.

I can't imagine why anyone would want to do that. I mean, he barely resembles a goose, much less multiple geese who are able to give support of a technical nature.

Was that sarcasm?

:?