PX156 - A2 - blackbody radiation and laws

F - black bodies and colours

blackbody

• an ideal blackbody is an object that absorbs all the radiation that strikes it
• it also radiates ideally

stefan-boltzmann law for blackbodies

where, $I=$ total intensity, $\sigma \approx 5.67\times {10}^{-}8W{m}^{-2}{K}^{-4}$

• power is not uniformly distributed across the spectrum, so a useful notation is spectral emittance: $I(\lambda )=$ intensity per wavelength, $\lambda$, interval
• total intensity, $I$, is the area under the $I(\lambda )-\lambda$ curve:

wien's displacement law

• number of moles in a small interval, $\delta n=\lambda \to \lambda -\delta \lambda :$