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In physics and many other areas of science and engineering the intensity or flux of radiant energy is the power transferred per unit area, where the area is measured on the plane perpendicular to the direction of propagation of the energy.
Radiant intensity: I: Power of emitted electromagnetic radiation per unit solid angle W/sr L 2 M T −3: scalar Reaction rate: r: Rate of a chemical reaction for unit time mol/(m 3 ⋅s) L −3 T −1 N: intensive, scalar Refractive index: n: Factor by which the phase velocity of light is reduced in a medium unitless 1: intensive, scalar Reluctance
Luminous intensity, a photometric quantity measured in lumens per steradian (lm/sr), or candela (cd) Irradiance, a radiometric quantity, measured in watts per square meter (W/m 2) Intensity (physics), the name for irradiance used in other branches of physics (W/m 2) Radiance, commonly called "intensity" in astronomy and astrophysics (W·sr −1 ...
Hence, the intensity of radiation passing through any unit area (directly facing the point source) is inversely proportional to the square of the distance from the point source. Gauss's law for gravity is similarly applicable, and can be used with any physical quantity that acts in accordance with the inverse-square relationship.
Examples of intensive properties include temperature, T; refractive index, n; density, ρ; and hardness, η. By contrast, an extensive property or extensive quantity is one whose magnitude is additive for subsystems. [4] Examples include mass, volume and entropy. [5] Not all properties of matter fall into these two categories.
Radiant intensity is used to characterize the emission of radiation by an antenna: [2], = (), where E e is the irradiance of the antenna;; r is the distance from the antenna.; Unlike power density, radiant intensity does not depend on distance: because radiant intensity is defined as the power through a solid angle, the decreasing power density over distance due to the inverse-square law is ...
Schwarzschild's equation is the formula by which you may calculate the intensity of any flux of electromagnetic energy after passage through a non-scattering medium when all variables are fixed, provided we know the temperature, pressure, and composition of the medium.
In physics, the term "light" may refer more broadly to electromagnetic radiation of any wavelength, whether visible or not. [4] [5] In this sense, gamma rays, X-rays, microwaves and radio waves are also light. The primary properties of light are intensity, propagation direction, frequency or wavelength spectrum, and polarization.