EM Wave Propagation

[Advaithi]

As a learner of Physics I am very much interested to know about the EM waves and EM field. As far as I know, the Electric filed and Magnetic filed are perpendicular to each other and that makes the EM field propagation. EM waves are fluctuations in that field. Radio waves, micro waves, IR,visible light,UV, X-ray, and Gamma rays are EM waves at various frequncy ranges. I want to know why do the frquency ranges vary? Which makes them to vary and how? are the electric and magentic fields are spread all over the universe? are they fade away when getting farther away from matter?

 

 

[swansont]

The frequency depends on how the EM wave was created. The naming convention is part of that, and is used for convenience.

[steevey]

As a learner of Physics I am very much interested to know about the EM waves and EM field. As far as I know, the Electric filed and Magnetic filed are perpendicular to each other and that makes the EM field propagation. EM waves are fluctuations in that field. Radio waves, micro waves, IR,visible light,UV, X-ray, and Gamma rays are EM waves at various frequncy ranges. I want to know why do the frquency ranges vary? Which makes them to vary and how? are the electric and magentic fields are spread all over the universe? are they fade away when getting farther away from matter?

 

 

 

 

 

Generally higher energy reactions mean higher energy results. If a material gets really hot from kinetic energy, then it can emit high frequency photons. It has to do with how the electrons in nuclei jump between orbitals, and there's also matter which convert into EM energy when particles decay or annihilate each other, in which case a lot of energy is stored and released in those systems.

Edited April 20, 2011 by steevey

[lemur]

Generally higher energy reactions mean higher energy results. If a material gets really hot from kinetic energy, then it can emit high frequency photons. It has to do with how the electrons in nuclei jump between orbitals, and there's also matter which convert into EM energy when particles decay or annihilate each other, in which case a lot of energy is stored and released in those systems.

Don't want to derail the thread, but could it help to answer this question by including the issue of what might cause the relationship between energy level change and the frequency of emission? E.g. if electrons are absorbing and re-emitting energy at a certain rate, and thus emitting radiation at a certain frequency, what is responsible for the given frequency and what allows it to occur only for certain frequencies in each element and not others?

Edited April 20, 2011 by lemur

[swansont]

Blackbody emission, i.e. radiation from thermal sources, is not tied directly in to electron transitions; it's a continuum rather than the discrete values you get from such transitions. The question of why you get different frequencies from those transitions is one of atomic structure, not EM waves and their propagation.

[lemur]

Blackbody emission, i.e. radiation from thermal sources, is not tied directly in to electron transitions; it's a continuum rather than the discrete values you get from such transitions. The question of why you get different frequencies from those transitions is one of atomic structure, not EM waves and their propagation.

I thought a perfect blackbody was a substance that absorbed and emitted all frequencies.

 

I thought that EM emissions always were the result of an electron dropping from a higher level to a lower one; and that photon absorption always resulted in an electron increasing levels.

 

 

To me it seems like substances behave like crystals with certain resonant frequencies at which they either vibrate or not, except whereas crystals are vibrating mechanically, the photon-emiting substances are vibrating electromagnetically. Is that a detrimental comparison?

[steevey]

Don't want to derail the thread, but could it help to answer this question by including the issue of what might cause the relationship between energy level change and the frequency of emission? E.g. if electrons are absorbing and re-emitting energy at a certain rate, and thus emitting radiation at a certain frequency, what is responsible for the given frequency and what allows it to occur only for certain frequencies in each element and not others?

 

You heat a substance up to 4000 degrees F and it emits visible light in the blue end of the spectrum. You heat a substance up to 100 degrees F and it emits infrared light which isn't visible to us. An electron and anti-electron collide and supposedly the matter of each cease to exist while two gamma rays result.

Edited April 21, 2011 by steevey

[swansont]

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Moderator Note

Discussion of details of atomic spectra moved http://www.scienceforums.net/topic/56628-atomic-spectra/

You heat a substance up to 4000 degrees F and it emits visible light in the blue end of the spectrum. You heat a substance up to 100 degrees F and it emits infrared light which isn't visible to us.

In both of those cases there is a range of frequencies being emitted. The object at 4000 ºF (~2500 K) is still emitting quite a lot in the IR; that's around the temperature of a light bulb filament, and most of the energy is not in the visible part of the spectrum. Here's what it looks like at even hotter temperatures



At 100 ºF the peak will be somewhere around 10 microns

I thought a perfect blackbody was a substance that absorbed and emitted all frequencies.

I thought that EM emissions always were the result of an electron dropping from a higher level to a lower one; and that photon absorption always resulted in an electron increasing levels.

A perfect blackbody is something with the ability to absorb or emit at all frequencies; that's why I said it was a continuum. The intensity profile depends on the temperature.

You also get EM radiation from the acceleration of charged particles, nuclear transitions, and, as steevey noted, annihilation reactions.