Practice portal › Electromagnetic Waves › Maxwell's Equations and the Production of EM Waves
Asked in GSEB Board March 2016 · Sources: the accelerated charge and Hertz
Idea: the field of an oscillating charge splits in two. The inductive, or near, fields fall as 1/(r³) and are a quarter of a cycle out of phase; the radiation fields fall as 1/r and are in phase.
At large r the steeply falling part has already vanished, so all that a distant receiver sees is the radiated component.
Its intensity then goes as E², that is as 1/(r²), which is just a fixed power spread over a sphere of area 4π r².
So the decrease is as per r⁻¹ and these are the radiated components.
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