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At large distance from the source E and B are in phase and the decrease in their magnitude is comparatively slower with distance r as per ___.

Asked in GUJCET 2019 · Sources: the accelerated charge and Hertz

Answer: (1) r⁻¹

Step-by-step solution

Idea: an oscillating charge has two zones. Close in, the induction fields dominate and die away very fast; far out, only the radiated part is left.

In that radiation zone the two fields stay in phase and both fall as 1/r.

That is exactly what a wave carrying energy outwards must do: the intensity goes as E², so it falls as 1/(r²), which is a fixed power spread over a sphere of area 4π r².

So the decrease follows r⁻¹.

Why the other options are wrong

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