part_of relative permittivity
In ___MASK21___ , electric flux is the measure of flow of the electric field through a given area . Electric flux is proportional to the number of electric field lines going through a normally perpendicular surface . If the electric field is uniform , the electric flux passing through a surface of vector area is where is the electric field ( having units of ), is its magnitude , is the area of the surface , and is the angle between the electric field lines and the normal ( perpendicular ) to . An ion is an ___MASK12___ or a molecule in which the total number of electrons is not equal to the total number of protons , giving the ___MASK12___ or molecule a net positive or negative electrical charge . Ions can be created , by either chemical or physical means , via ionization . In electricity ( ___MASK21___ ), the electric susceptibility formula_1 ( latin : " susceptibilis "  receptive ) is a dimensionless proportionality constant that indicates the degree of polarization of a dielectric material in response to an applied electric field . The greater the electric susceptibility , the greater the ability of a material to polarize in response to the field , and thereby reduce the total electric field inside the material ( and store energy ). It is in this way that the electric susceptibility influences the electric permittivity of the material and thus influences many other phenomena in that medium , from the capacitance of capacitors to the speed of light . In ___MASK21___ , permittivity or absolute permittivity is the measure of resistance that is encountered when forming an electric field in a medium . In other words , permittivity is a measure of how an electric field affects , and is affected by , a dielectric medium . The permittivity of a medium describes how much electric field ( more correctly , flux ) is ' generated ' per unit charge in that medium . More electric flux exists in a medium with a low permittivity ( per unit charge ) because of polarization effects . Permittivity is directly related to electric susceptibility , which is a measure of how easily a dielectric polarizes in response to an electric field . Thus , permittivity relates to a material ' s ability to resist an electric field ( while , unfortunately , the word stem " permit " suggests the inverse quantity ). ___MASK21___ is a branch of physics involving the study of the electromagnetic force , a type of physical interaction that occurs between electrically charged particles . The electromagnetic force usually exhibits electromagnetic fields such as electric fields , magnetic fields , and light and is one of the four fundamental interactions ( commonly called forces ) in nature . The other three fundamental interactions are the strong interaction , the weak interaction , and gravitation . The relative permittivity of a material is its dielectric permittivity expressed as a ratio relative to the permittivity of vacuum . Permittivity is a material property that affects the Coulomb force between two point charges in the material . Relative permittivity is the factor by which the electric field between the charges is decreased relative to vacuum . Likewise , relative permittivity is the ratio of the capacitance of a capacitor using that material as a dielectric , compared to a similar capacitor that has vacuum as its dielectric . Relative permittivity is also commonly known as dielectric constant , a term deprecated in ___MASK76___ and engineering , but one which is still commonly used in chemistry .