electromagnetic waves

[blinkyblinky]

How do they transfer energy through a vacuum?

[blinkyblinky]

ooops, wrong category

[jake-the-peg]

Seeing as I was in B&S let me see if I can give you an answer.

An accelerating electric charge generates a magnetic field as the magnetic field builds it generates an electric field which inturn generates a magnetic fieled etc. So you get a small pulse of alternating electric and magnetic fields.

We call them waves because they share some of the properties of waves but they can also behave like particles or photons. You might ask whether light is wave-like or particle-like the answer is neither it's light-like.

Incidently all this alternating field stuff was worked out by a really smart chap called James Clarke-Maxwell - I've heard it speculated that he was the last person to fully understand all current knowlege on physics and that after his time there was just too much for any single person to completely appreciate.

[Strippy]

Would i be right in thinking that some forms of energy can travel through a vacuum, radiation in particular?

[jake-the-peg]

Absolutely all the 4 forces operate in vacuums and have energy associated with them so electromagnetic waves carry energy proportional to their wavelength so radiowaves have lower energy compared to light and x-rays have more still all the way up to gamma waves at the top of the spectrum.

Gravity also exerts a force in a vacuum - it's what keeps the moon going around the earth and there is a gravitational potential energy associated with that.

The other 2 forces the strong and weak operate at subatomic ranges so vacuum is fairly meaningless.

A lot of people seem to have a strange idea of what energy is and have some sort of concept of pure energy.

In fact energy is a property of a body like it's mass or colour. When somebody uses the word energy replace it with the word weight and see if it makes sense - eg. - That ball has a lot of weight (ie is heavy) makes sense - It is composed of pure weight does not

[blinkyblinky]

Thanks for your answer Jake.

The thing I'm having trouble with is this:

I can see that energy can be transfered through water, with water molecules interacting with their neighbouring water molecules and sending out ripples in this way. The same for air. But how do waves travel through a vacuum when there is no stuff to be affecting neighbouring stuff?

[jake-the-peg]

That's because you're being mislead by the term waves.

Light does behave like waves in some ways - it refracts (changes direction as it goes through denser material) ad diffracts (bends around obstacles) So people thought like you that it must be a wave in something. This something was even given a name the ether. A couple of scientists called Michaelson and Morely finally proved it didn't exist in 1887.

This is why I say that light is neither a wavelike or particle-like (which it cal also act like) but light-like.

You could think of it as a little packet of alternating electric and magnetic field but it's a problem that occupied some of the greatest minds of the 20th century so if you're having trouble with it you're in good company

[blinkyblinky]

But radio waves also work through a vacuum, don't they?

[jake-the-peg]

Absolutly - they are another form of light.

if you imagine a wave like shaking a skipping rope attached to a drainpipe the faster you shake it the smaller the distance gets between the peaks of the waves.

With electromagenetic waves a large distance gives you a radio-wave. As the frequency gets faster and the wavelength shorter you get microwaves, then infra-red then red light then all the colours up to blue and violet then ultra violet, x-rays all the way up to gamma rays.

As the wavelength gets shorter the "skipping rope" is shaken faster which means the waves get more energetic which is kin of why x rays and gamma rays can do you such harm if you're exposed to them too much

[blinkyblinky]

Thanks Jake, you explained that very well.

I still can't picture in my mind a thing which is both a particle and a wave, or behaves like both, or is something completely different but exhibits wave-like and particle-like properties depending on the medium (in space it's a particle, in glass it's a wave...) weird.