Electromagnetic radiation (EMR) threshold

AI Thread Summary
The discussion clarifies that there is no specific threshold energy or frequency for an electromagnetic field to transition from near-field to far-field. Instead, the transition depends on distance from the source, with both near-field and far-field components present at varying distances. The near-field component diminishes rapidly as one moves away from the source, becoming negligible beyond a few wavelengths. Understanding this concept is crucial for analyzing electromagnetic radiation behavior. Overall, the relationship between near-field and far-field is defined by distance rather than a fixed threshold.
Homestar1
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What is the threshold energy (or frequency) required for an electromagnetic field to transition from a near field to become self propagating (EMR), far field? (If I'm using the right definitions to ask the question correctly). Is this constant or are there other details needed to calculate this?
 
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There is no threshold. Given some distance from the source, some portion of the field will be near-field and some will be far-field, with the near-field falling off extremely rapidly as distance increases. Once the distance is more than a few wavelengths, there is virtually no near-field left.
 
Ah, that makes sense! Thanks so much!
 
Thread 'Motional EMF in Faraday disc, co-rotating magnet axial mean flux'

Thread 'Motional EMF in Faraday disc, co-rotating magnet axial mean flux'

So here is the motional EMF formula. Now I understand the standard Faraday paradox that an axis symmetric field source (like a speaker motor ring magnet) has a magnetic field that is frame invariant under rotation around axis of symmetry. The field is static whether you rotate the magnet or not. So far so good. What puzzles me is this , there is a term average magnetic flux or "azimuthal mean" , this term describes the average magnetic field through the area swept by the rotating Faraday...
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