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When we speak of electromagnetic waves, we think of oscillating waves. But all disturbances need not be oscillating at a frequency. For example, if I take water, I could just lower the bottom plate and cause a cavity at the middle of a pool, and that disturbance would propagate outward as a decrease in amplitude, but not as an oscillating wave with a crest and a trough.

For electrons, I would imagine achieving this by uniformly accelerating a charge (as opposed to AC where the acceleration is sinusoidal, sawtooth, etc., so it accelerates and decelerates). It is only said that accelerating charges radiate, nothing is said about the mode of acceleration.

I understand that natural processes will be in the form of random vibrations, but as humans we are able to create DC for our purposes. I also know DC is fundamentally AC, but the ripple effect is minimal and it is the power that matters.

What is special about radiation with a frequency as opposed to other non-oscillating forms of radiation? Why do we always talk in terms of frequencies when referring to radiations?

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    $\begingroup$ I believe you're right that radiation fields will form with any acceleration. If you keep accelerating only in 1 direction and never reverse, the radiation fields will grow larger and larger. For example, if accelerated along the x-axis, you'd probably get larger and larger fields, happening be tangent to an imaginary expanding circle around the accelerating charge. These radiation fields will propagate by induction (the imaginary circle the fields are tangent to expands over time) and be detectable with a radiation detector. $\endgroup$
    – Daniel
    Commented Feb 2 at 17:24
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    $\begingroup$ But since the particle is accelerated in one direction always, the radiation fields around the imaginary expanding circle will always be either clockwise or counter-clockwise (never flip direction). The best treatment of this is in an appendix of a book by Purcell and Morin. $\endgroup$
    – Daniel
    Commented Feb 2 at 17:26
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    $\begingroup$ But to your point - yes, a radiation detector will be able to detect these radiation fields, even if they aren't a wave, but mostly increases in amplitude over time. They are detectable because the so called Poynting vector shows these fields to transfer energy (they captured energy from the particle when originally forming). $\endgroup$
    – Daniel
    Commented Feb 2 at 17:33
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    $\begingroup$ for sufficiently high enough intensities our heart and brain are sensitive to frequencies below 1000Hz but don't experiment with it at home. $\endgroup$
    – hyportnex
    Commented Feb 2 at 17:57
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    $\begingroup$ In my careless youth I made some mistakes around 60Hz both in the lab and in the kitchen, but it is better not to remember them. $\endgroup$
    – hyportnex
    Commented Feb 2 at 18:22

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The light that comes from the sun comes in the form of oscillation of the EM field in the range of 100's of terahertz and our eyes evolved to take advantage of that.

There's nothing "wrong" with other forms of disturbance of the EM field, they're just not the ones that our eyes evolved to detect.

Why do we always talk in terms of frequencies when referring to radiations?

If you mean, why do we so often analyze disturbances of the EM field as combinations of sinusoidal (or complex exponential) disturbances, it's because the solutions to Maxwell's equations and the wave equation are easily found with these forms, and from Fourier analysis we know that these solutions can be used to construct any other solution we are interested in.

Furthermore, the complex exponentials (with sinusoids as a subset) are eigenfunctions of the wave equation, meaning that if we find a complex exponential solution for a problem at one point in space it's easy to find how this wave propagates to other points in space over time. With other forms of solution the easiest way to find how they propagate is to deconstruct them into complex exponentials using the Fourier transform, propagate those solutions, and then rre-construct the solution at the later time.

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  • $\begingroup$ Perhaps I should've edited the question for contexts other than just the eyes $\endgroup$ Commented Feb 2 at 17:11

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