Electromagnetic wave is energy radiation that consists of electric and magnetic fields perpendicular to each other. Electromagnetic wave is produced by electric charge acceleration or magnetic field variation. In vacuum, electromagnetic wave travels at the speed of light (notation: ), that is 300,000 kilometers/second or 186,000 miles/second. Electromagnetic spectrum encompasses all types of electromagnetic radiation. In general, in the order from the lowest to the highest frequency or from the longest to the shortest wavelength, it can be classified to: - radio wave (ELF, SLF, ULF, VLF, LF, MF, HF, VHF, UHF, SHF, EHF) - microwave (SHF, EHF) - infrared light (300 GHz - 400 THz) - visible light ( 400 THz) - ultraviolet light - x-rays - gamma rays Electromagnetic radiation is described in two equations below: = Î»f where : the speed of light, : wavelength, : frequency = hf where : photon energy, : Planck's constant, : frequency The first is for electromagnetic radiation as a wave, and the second as particles. EM is the shorthand of electromagnetic.