Electromagnetic radiation travels in wave form. All electromagnetic waves travel at the speed of 299.793 km/sec in a vacuum and very nearly the same speed in air. In quantum physics electromagnetic radiation is also described in terms of particles called photons whose energy is given by the equation E = hf where h is the Planck constant and f the frequency of corresponding wave. Electromagnetic wave propagation is fully described by the Maxwell Equations that unified in 1860s the laws of electricity and magnetism.