Solid angle of its faces is one-sixth of that, or sr. Solid angles can also be measured in square degrees (1 sr = () square degrees), in square minutes and square seconds, or in fractions of the sphere (1 sr = fractional area), also known as spat (1 sp = 4 sr). In spherical coordinates there is a formula for the differential, where is the colatitude (angle from the North pole) and is the longitude. The solid angle for an arbitrary oriented surface S subtended at a point P is equal to the solid angle of the projection of the surface S
Polymeric surface processing proclude it from being a competitive surface modification method within industry. The process begins with production of plasma via ionization either by deposition on monomer mixtures or gaseous carrier ions. The power required to produce the necessary plasma flux can be derived from the active volume mass/energy balance: formula_1 where formula_2 where formula_3 denotes the surface energy of the solid–liquid, liquid–gas, or solid–gas interface formula_4 is the measured contact angle A series of solutions with known surface tension (e.g., Dyne solutions) can be used to estimate the surface energy of the polymer substrate qualitatively by observing the wettability of