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I was just thinking again about another aspect of electromagnetic waves: Assume we have a planar wave. How "broad" is it or how far does the electric field of it reach? For instance if we have a single planar wave, assume the k-vector in the direction of propagation and then the electric field-vector is normal to it in vacuum. now if the planar wave hits a plane perpendicular to the k-vector, lets say a plane consisting of infinitely many little dipoles how far would the electric field of the planar wave affect the dipoles? only at the "point" where it hits or somehow radially decreasing with 1/r^2?

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# I Electromagnetic waves: How broad is a plane wave?

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