Electric field strength is a quantitative expression of the intensity of an electric field at a particular location. The standard unit is the volt per meter (v/m or v • m ^-1). A field strength of 1 v/m represents a potential difference of one volt between points separated by one meter. Any electrically charged object produces an electric field. This field has an effect on other charged objects in the vicinity. The field strength at a particular distance from an object is directly proportional to the electric charge, in coulomb s, on that object. The field strength is inversely proportional to the distance from a charged object. The field-strength-vs-distance curve is a direct inverse function, and not an inverse-square function, because electric field strength is specified in terms of a linear displacement (per meter) rather than a surface area (per meter squared). An alternative expression for the intensity of an electric field is electric flux density. This refers to the number of lines of electric flux passing orthogonally (at right angles) through a given surface area, usually one meter squared (1 m (2). Electric flux density, like electric field strength, is directly proportional to the charge on the object. But flux density diminishes with distance according to the inverse-square law, because it is specified in terms of a surface area (per meter squared) rather than a linear displacement (per meter). Sometimes the strength of an electromagnetic field (EM field) is specified in terms of the intensity of its electric-field component. This is done by engineers and scientists when talking about the radio-frequency field strength at a certain location arising from sources such as distant transmitters, celestial objects, high-tension utility lines, computer displays, or microwave ovens. In this context, electric field strength is usually specified in microvolts per meter (µV/m or µV • m ^-1), nanovolts per meter (nV/m or nV • m ^-1), or picovolts per meter (pV/m or pV • m ^-1). Also see: Coulomb, EM field, meter, volt, and SI (International System of Units)