Electromagnetic radiation and B fields in EMR are in-phase (see math section below). An important aspect of light's nature is its frequency. The frequency of a wave is its rate of oscillation and is measured in hertz, the SI unit of frequency, where one hertz is equal to one oscillation per second. Light usually has multiple frequencies that sum to form the resultant wave. Different frequencies undergo different angles of refraction, a phenomenon known as dispersion. A wave consists of successive troughs and crests, and the distance between two adjacent crests or troughs is called the wavelength. Waves of the electromagnetic spectrum
Sound power temperature, the sound power level at distance "r" from the sound source is approximately related to sound pressure level (SPL) by where Derivation of this equation: For a "progressive" spherical wave, where "z" is the characteristic specific acoustic impedance. Consequently, and since by definition , where is the reference sound pressure, The sound power estimated practically does not depend on distance. The sound pressure used in the calculation may be affected by distance due to viscous effects in the propagation of sound unless this is accounted for. Sound power Sound power or acoustic power is the rate at which sound