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I read that the accelerated charges create electromagnetic field/spectrum which consists of following different waves:

gamma, X-rays, ultraviolet, visible light, infrared, microwaves, & radio waves

gamma,ultraviolet and x-rays are injurious to human so why humans are not effected by them during normal transmission of electricity as electricity is all around us. Plus only radio waves and microwaves are mostly used for communication. So how these waves are picked up from the spectrum for communication ?

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  • $\begingroup$ The term gamma ray is usually reserved for photons emitted through processes involving atomic nuclei, not electrons. The rest of the question is very broad, and indicates that you have put very little effort into researching the background of the question. $\endgroup$ – Jon Custer May 3 '16 at 19:15
  • $\begingroup$ isnt these waves are in electromagnetic spectrum ? when charges are accelerated isnt all these electromagnetic waves are created ? someone just told me " The key element is how quickly the charges are accelerated; this determines the wavelength and hence their danger to humans. " $\endgroup$ – Alex May 3 '16 at 19:19
  • $\begingroup$ Yes, gammas are photons. So are X-rays, and their energy ranges overlap. Nonetheless, the two terms are deliberate - gammas are generated through processes in a nucleus (transitions between nucleus energy levels), and X-rays through electronic processes (transitions between electronic configurations). $\endgroup$ – Jon Custer May 3 '16 at 19:24
  • $\begingroup$ so all these electromaagnetic waves are created in different ways ? how radio waves and microwaves which are used for communication are created then ? $\endgroup$ – Alex May 3 '16 at 19:27
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    $\begingroup$ so when ac current flows to create radio waves it does not produce x.rays and gamma waves and the whole electromagnetic spectrum as well ? $\endgroup$ – Alex May 3 '16 at 20:15
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The electromagnetic radiation of gamma rays and X-rays is generated through accelerative processes involving atomic nuclei. The involved photons are the so called hard radiation and could destroy human tissue. The acceleration of electrons generates photons in the range of UV radiation, visible radiation and IR radiation.

It is possible to send informations by EM radiation of any wavelength. So X-ray pulsars are rotating and this information we receive. In this example the direction of the EM radiation gets changed and by this we receive periodical signals from which we extract informations about the speed of the stars rotation. IR radiation is used in the fiber-optics communikation and the information transfer happens by pulses too.

The mechanism behind radio waves is different from the above-described pulse processes. It is a so called modulated EM radiation. An electronic (or in the past an electric) device generates mostly sinusoidal oscillations. So electrons inside an antenna rod get accelerated through he power of the antenna generator. But their way along the rod during the acceleration period is much shorter than the antenna rods lenght. Furthermore the frequency of the generator (by a constant lenght of the antenna rod) can be variable (by loss of efficiency), by this the involved electrons get accelerated different and by this this electrons emit photons of different wavelenghts.

This, the photons wavelength, has nothing to do with the classification of radio waves from the generator frequency and the length of the antenna rod. It could be dangerous to stay by an antenna generator or the rod, they could emit X-rays. The same holds for the radar. The classification (modulation the radiation) of radars run from meters to mm, but the X-ray emission as well as the IR-radiation from the involved electrons is remarkable.

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  • $\begingroup$ so we need different techniques to generate these different types of electromagnetic waves ? $\endgroup$ – Alex May 4 '16 at 8:07
  • $\begingroup$ @Alex One use LEDs, lasers, bulbs, X-Ray devices and so on to emit EM radiation. And one use different electronic devices to modulate EM radiation. $\endgroup$ – HolgerFiedler May 4 '16 at 9:52
  • $\begingroup$ so different conditions are required to create different electromagnetic waves or more than one electromagnetic waves at the same time ? right ? $\endgroup$ – Alex May 4 '16 at 9:56
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Each of those spectral regions involve electromagnetic waves (photons) at a range of frequencies, and it is that which determines how they are generated, how they interact with matter (i.e. Particles with charge, one by one or in various groupings and configurations like atoms, molecules, bulk material composed of different molecules, different temperatures, different phases etc), and thus the use we can make of them.

Radio waves are generated by transistors but also vacuum tubes and other devices, and also natural phenomena like lightning and astrophysical phenomena. The freq range from a few kilohertz to about 1-2 GHz Does not Get absorbed much by the things in our environments too much and therefore can travel longer distances useful for communications. Lower freq diffract around our normal objects (trees, people, houses, etc) and thus propagate with less attenuation, but do exhibit other issues like multipath. It is all relative to sizes and the propagating environment. Freqs above 20 GHz get absorbed a lot by water vapor and rain, and so at 20/30 GHz used for eg satellite TV (eg direcTV) you can loose the link on heavy rain.

There is a lot more to selecting the best freq for anything, involving those kinds of interactions, and other factors such as available bandwidth and technology to see them and process them. For astrophysical observations they each are caused by different physical processes and energies. For wireless comms and radars and remote sensing you have to take all those into account.

And yes, the freq which is proportional to the photon energy is what mostly determines if the interactions with the molecules in our bodies will affect or destroy those molecules, and thus be dangerous. The higher freqs like x rays do some damage that's why you want to limit how many x rays you take, and gamma rays which are higher freq (and more energetic, often from nuclear or subnuclear processes) are the most destructive.

BTW, normal electricity in household AC is usually at 60 Hz, too low a freq to radiate anything at all unless you build a humongous antenna. So they only thing that can kill you is then the current flowing through you if you stick your fingers in the socket.

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