Wednesday, 2 September 2020

electromagnetism - What change in an EM field is required to create an EM wave?


From here



To generate a long wavelength requires an aerial of roughly one wavelength in size.



and here



One of the difficulties posed when broadcasting in the ELF frequency range is antenna size, because the length of the antenna must be at least a substantial fraction of the length of the waves.




I gather that a charge has to be moved along a straight distance similar to the wavelength of an EM wave to generate an EM wave of that frequency.


If a straight conductor has wavelength in size, does an electron have to move from one end to the other and back to generate the wave ?


This seems totally different than the distances involved in electron jumps between electron orbitals for generating a given wavelength.


Regardless of the above assumptions being true or false please detail: What are the movement, speed and accelleration of a charge required to generate an EM wave of a given wavelength?


related: How do near-field EM fields change to far-field EM waves at an antenna


EDIT: Although answers here shed light on the mistakes of my assumptions, none provides a clear answer to the question in bold. I had to to ask another question to get the proper answer : a charge oscillating in space at a given frequency will generate an EM wave of the same frequency




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