Electromagnetic waves can propagate both in any medium and in a vacuum. Vectors E, B, c are perpendicular to each other. These vectors form the right triplet of vectors i.e. if you rotate the grip handle in the direction from vector K to vector B, then it will move along the velocity vector from the wave. Since the vectors of intensity and magnetic induction are perpendicular to the direction of wave propagation, the electromagnetic wave is transverse.
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