some more thermo

content/physics/thermodynamics.md

@@ -38,3 +38,23 @@ $$
 - the subscript `mol` notates the same variable, but in units *per* mole. 
 - ==You might see both==, at least they were both on the concept builders.
 
+# Black-body radiation
+
+All objects/bodies emit electromagnetic radiation over a range of wavelengths. Cooler objects emit less radiation than warmer bodies, simply because of having less energy. An increase in temperature directly correlates with a smaller wavelength ($\lambda$), and a higher frequency ($f$ or $v$).
+
+Radiation being *incident* means that it strikes or falls upon a surface, object, or body. Radiation that is incident on an object is partially absorbed and partially reflected. **Thermodynamic Equilibrium** is a state in which a body emits radiation at the same rate that radiation hits it. Therefore, a good absorber of radiation is also a good emitter. A perfect absorber absorbs all E.M. radiation incident on it. Such an object is called a *black body*. This doesn't mean no energy is emitted, however. A black body remits the radiation it absorbs as a thermal radiation in a spectrum determined solely by its temperature. 
+
+The intensity of the remissions of a black body is given by a function defined so:
+$$
+I(\lambda,T)
+$$
+
+Where $I$ is the *power* intensity that is radiated per unit of wavelength $\lambda$, per unit area of the black body. By multiplying the differential of $\lambda$:
+
+$$
+I(\lambda, T)\mathrm{d}\lamdba
+$$
+
+Provides the power per unit area of the black body, from the interval $\[\lambda, \lambda + \mathrm{d}\lambda\]$, given that $\mathrm{d}\lambda$ is an infinitesimally small quantity. 
+
+