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LAN_403

ConKbot of Doom

Mon May 16 2011, 02:02PM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
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Posts: 329

Makes sense, since a square wave would just be all the odd harmonics. But given that our eye only covers 400-800Thz (roughly) it'd be difficult to see the 2nd harmonic in anything other then deep red light, as your harmonics would be getting deeper and deeper into the UV region

magnet18

Tue May 17 2011, 01:35AM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
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Posts: 624

To add to this, whats the difference between electromagnetic radiation released from an antenna and electromagnetic radiation from an LED?
since LED's give off light one photon at a time, and antennas broadcast continuously?

Mattski

Tue May 17 2011, 02:58AM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

It's the same, all EM radiation from radio waves to light waves is both a particle and a wave. The particle nature of radiation helps explain certain things like the photoelectric effect and single photon interference. But most stuff can be well described by the wave perspective. Photons are being emitted, but there are so many of them that the quantized nature isn't significant (under typical radio conditions).

Hyperphysics has a nice description of the dual nature:

Pinky's Brain

Tue May 17 2011, 10:08AM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837

It behaves like both a particle and a wave at some level of understanding of particles and wave behaviours.

Although it's mostly an artefact of the way we learn physics ... it's easier for us to think in terms of particles than in term of quantization effects (which are just plain unintuitive, you'd almost start thinking the universe is just a massive FEM simulation).

Steve Conner

Wed May 18 2011, 09:20AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Well, according to Douglas Adams, it is, and it's run by mice.

wrote ...
Although often mistaken for a planet, Earth is in reality the greatest supercomputer of all time, designed by the second greatest supercomputer of all time, Deep Thought, to calculate the Ultimate Question of Life, The Universe And Everything (to which the answer is 42).

radiotech

Thu May 19 2011, 08:59PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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It just might be the most of our universe is composed
of stuff that that has no electrons. It is quite easy for a hydrogen
atom to lose the only one it has.

Things that have electrons, seem to be able to see other
things similarly endowed.

But is always is easier to find what you seek under the lamp post
in the dark, isn't it?

Ash Small

Sun May 22 2011, 01:56PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

radiotech wrote ...

It just might be the most of our universe is composed
of stuff that that has no electrons. It is quite easy for a hydrogen
atom to lose the only one it has.

Things that have electrons, seem to be able to see other
things similarly endowed.

But is always is easier to find what you seek under the lamp post
in the dark, isn't it?

Try googling 'electric cocmos' or 'electric universe'.

While some of it might seem to border on pseudoscience, there is a lot there that makes a lot of sense, but you may need to dig a bit to find it..

Meatball

Wed May 25 2011, 12:46AM

Registered Member #2401 Joined: Mon Sept 28 2009, 04:25PM
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Posts: 74

If all EM waves can only be created by the acceleration of charges, what then would the acceleration of the charge be, that produced a square EM wave?

I'm not sure that is even possible, considering the field magnitude would peak as the charge's acceleration peaks. So with a square wave, the charge would have to have a near instant change in position to maximize the slope of the increasing E field.

How does one so quickly bump an electron, and then bring it to such a short halt again?

Inducktion

Wed May 25 2011, 01:00AM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Meatball wrote ...

If all EM waves can only be created by the acceleration of charges, what then would the acceleration of the charge be, that produced a square EM wave?

I'm not sure that is even possible, considering the field magnitude would peak as the charge's acceleration peaks. So with a square wave, the charge would have to have a near instant change in position to maximize the slope of the increasing E field.

How does one so quickly bump an electron, and then bring it to such a short halt again?

Easy. Bump it forward, then bump it backwards again with a bump of equal magnitude.

Pinky's Brain

Wed May 25 2011, 02:19AM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837

wrote ...

If all EM waves can only be created by the acceleration of charges, what then would the acceleration of the charge be, that produced a square EM wave?

Can't be done ... a square EM wave is actually just a summation of coherent light of different wavelengths, the electron can only emit one photon at a time.

I think you're misunderstanding the bit about acceleration. Now I have a purely conceptual understanding of QM, because I'm far too lazy to do all the math ... but AFAICS it's not the vibration of the electron which generates the EM, it's the quantum leap from one velocity to another which generates the photon (in essence the velocity step is stochastic and thus generates a photon of random wavelength, but the wavefronts of acceleration/deceleration set up in the antenna cause amplified stimulated emission ... antennas have a lot in common with lasers).

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