Electromagnetism and its forms

[Rasori]

I think this belongs in one of the mechanics threads, and I'm pretty sure it fits here, but feel free to move it.

 

Anyways, I know that things like radio waves, light, and microwaves all fit under the Electromagnetism category. I'm curious to know what fits under the same category, so anyone interested in making/contributing to a list would be welcomed. Also, if someone could give me a basic reason why these fit under the same category, that'd be nice. I'll try my best to understand it.

 

Plus, are there ways to convert between these forms? Can you, for example, convert radio waves to visible light? Or could you possibly piggyback these things, like by (ignore practical uses, just can this be done) putting light waves on with the radio waves in order to make the waves visible?

 

I don't know where I'm headed with this, and I don't know that anyone wants to find out, but it always is nice to know

[ecoli]

http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html

[Ophiolite]

Can you' date=' for example, convert radio waves to visible light? Or could you possibly piggyback these things, like by (ignore practical uses, just can this be done) putting light waves on with the radio waves in order to make the waves visible?

[/quote']

Think TV.

Real World >>> Light >>> Camera >>> Electric Signal >>>Radio Wave >>> TV >>>> Light >>> RealWorld (Your eyes)

[Rasori]

Interesting. So the magnetism in an electromagnet isn't related to the electromagnetic spectrum? I had assumed it was, but now I'm uncertain.

 

And thank you for that good point about TV, Ophiolite.

[5614]

So the magnetism in an electromagnet isn't related to the electromagnetic spectrum? I had assumed it was, but now I'm uncertain.

 

no they are not related;

 

magnetic fields (from magnets),

electrical currents (from batteries) &

electromagnetic spectrum (EM spec. like light etc)

 

are not really related... you could start talking about how radios pick up signals and stuff like that, but they are not really the same thing.

 

think of it this way:

 

magnetic field is made up of a magnetic field

electrical current made up of flowing electrons

electromagnetic waves are made up of photons.

[bh_doc]

It's not quite the same thing, but it is definitely related. (Magnetic and electric fields are propagated via EM, are they not?)

 

Take light. Light is a wave. Light has a frequency. Humans can see a range of these frequencies. Some animals can see ranges of frequencies different to humans. Now what about those frequencies beyond that which humans can see? This is where all those other things you mentioned turn up. They are just light (technically electromagnetic) waves of different frequencies that we can't see. That's how they fit in.

[JaKiri]

no they are not related;

 

magnetic fields (from magnets)' date='

electrical currents (from batteries) &

electromagnetic spectrum (EM spec. like light etc)

 

are not really related...[/quote']

 

Except that magnetic and electrical fields use photons as the exchange particle.

 

Can you, for example, convert radio waves to visible light? Or could you possibly piggyback these things, like by (ignore practical uses, just can this be done) putting light waves on with the radio waves in order to make the waves visible?

 

Changing the wavelength can be done (doppler shift, for example). And you can't really piggyback radio and visable light, because visable light doesn't have the properties of the radio wave that let it be transmitted for the distances it is.

[YT2095]

however you Could modulate a visible frequency with a radiowave, using light as the carrier, but it would still be far too fast of a "Flicker" to see.

 

IR remote controls (like the one for your TV set) modulates IR light at a freq in the radio band (about 200khz).

 

Fiber Optic cables do it all the time as well

[swansont]

EM radiation is, specifically, mutually inducing oscillating electric and magnetic fields. If you look at Maxwell's equations with the time components, you will see that B ~ dE/dt and E ~ dB/dt. So an oscillating E will induce a B, and an oscillating B will induce an E. If the oscillation is e.g. sinusoidal, then the changing E will induce a changing B that then induces a changing E, and so on. The wave propagates.

 

DC fields don't do this.

 

---

 

As far as combining the radiation, you can also do this in nonlinear crystals in a process called four-wave mixing. You can add two frequencies and get the sum frequency as a result. You can also get the difference frequency. If the two inputs are the same frequency you call it second-harmonic generation (no difference frequency output , of course)

 

You could, in principle, do this in multiple stages to get from RF to visible, but it would be incredibly inefficient.

[Rasori]

All very interesting and useful remarks, I thank you. I especially caught on to Jakiri's comment, however, of:

"...magnetic and electrical fields use photons as the exchange particle."

This might be a little off-topic, but I don't entirely understand the concept of photons being used as the exchange particle. Could someone explain what exchange particle is technically meaning?

[swansont]

This might be a little off-topic' date=' but I don't entirely understand the concept of photons being used as the exchange particle. Could someone explain what exchange particle is technically meaning?[/quote']

 

Virtual photons. Because they are massless, they can have an infinite range.

 

Virtual particles and photons as exchange particles here. Be warned, this isn't "See Spot run"

[Rasori]

So are the virtual photons unrelated to the photons used in light, or are they one and the same?

[swansont]

They are the same - a photon is a photon - but being "virtual" brings with it certain conditions.

[Rasori]

Are these conditions too technical to explain to me, or did you just not care to?

[swansont]

I posted a link before.

[Rasori]

Ah, I'll have to read it more carefully, but I hadn't gathered the conditions. But then, I suppose the whole thing is about the conditions, isn't it?

[Mart]

Think TV.

Real World >>> Light >>> Camera >>> Electric Signal >>>Radio Wave >>> TV >>>> Light >>> Real World(Your eyes)

 

I get Real World >>> Light >>> Camera >>> Electric Signal >>>Radio Wave >>> TV >>>> Light

 

but the last bit >>> Real World(Your eyes) how does that work?

[Rasori]

Well, I assume that's just the fact that the light is being received by your eyes.

[Mart]

Well, I assume that's just the fact that the light is being received by your eyes.

 

Thanks. I realise now that my question ends there because this is a physics forum and the rest of the explanation belongs in some other forum.

[Sayonara]

I suppose that depends on the level at which you want to study the mechanisms.

[Mart]

I suppose that depends on the level at which you want to study the mechanisms.

 

I want to know how the light that enters the eye (as physics would have it) gets converted into an experience of the outside world.

[Sayonara]

Out of curiosity, or to continue the redundant criticism?

 

If the former, I seem to recall there was an excellent description of the process in another thread. I will try to find it.

[Sayonara]

Gah.

 

It's not in the search results for "eye nerve" or "human eye", and a search for "eye" returns 16 pages of threads.

[Mart]

Out of curiosity' date=' or to continue the redundant criticism?

 

If the former, I seem to recall there was an excellent description of the process in another thread. I will try to find it.[/quote']

 

I don't understand what you mean by "redundant criticism". I appreciate your help in finding the thread.

[Sayonara]

Ignore it - I misinterpreted post #17.