Wave propagated through space from an oscillation source consisting of a magnetic field and an electric field perpendicular to each other.

【理】电磁波。电磁波是一种横波，是电场和磁场在空间的振动。电磁波可以在真空或在介质中传播。真空中电磁波速，为一常数 c = 3.00 * 10 ⁸ms^-1，是宇宙中最快的速度。可见光、微波和伽玛射线等都是电磁波。