 In practice, one directly controls by the voltage applied to the material through electrodes, and the work function is generally a fixed characteristic of the surface material.Consequently, this means that when a voltage is applied to a material, the electrostatic potential produced in the vacuum will be somewhat lower than the applied voltage, the difference depending on the work function of the material surface.Rearranging the above equation, one has
where is the voltage of the material (as measured by a voltmeter, through an attached electrode), relative to an electrical ground that is defined as having zero Fermi level.