*Check out the beginner's document!* [[Heat Transfers (Thermo)#Radiative Processes - The Stefan Boltzmann Constant|Click on this to go to it.]] # The View Factor - Intro to Incidence # Actually Defining a "Black Body" Strictly speaking, a black body absorbs all radiation incident on itself. That also means that they don't lose energy when they radiate! An example of this is a star... Basically, an object with an albedo of 0! # Thermal Radiation / Thermal Energy Remember from [[Kinetic Theory & Ideal Gases (Thermodynamics)#Translational Kinetic Energy|the ideal gases' doc]] that the equation for thermal energy is defined as: $E_{T} = \frac{3}{2}k_{B}T$ Where: - $k_B$ is Boltzmann's constant - $T$ is the temperature of the object. In actuality, this is a direct offshoot of the **Virial theorem**, which is an extension of the potential energy theorem for uniform black bodies. This makes thermal energy the potential energy of the black body. ## Defining the Black Body Radiator A perfect absorber/emitter of radiation! # The Prelude - The Ultraviolet Catastrophe //find rayleigh-jeans lore here! add wien lore too with the equation. However, a question still persists - how can we find the *wavelength* of the light emitted by an object at a certain temperature? One early attempt ## Wien's Law $nmK$ --> Temperature unit (unit kelvin!!!!) IT'S A GENERIC UNIT $\lambda_{max} = \frac{3 \times 10^6nm \cdot K} {T}$ ## The Rayleigh-Jeans Law - The Ultraviolet Catastrophe This'll build us up to our final boss battle... # Blackbody Radiation - Planck's Odyssey You're standing before a hulking mass of quantum physics, shuddering in your boots as the notion of hundreds, if not thousands of unintelligible equations fly past you. Let's try to demystify this! Given a temperature $T$ we can find an emission function of a black body (with temperature and frequency) $B(\nu ,T) = \frac{2hv^3}{c^2} \frac{1}{e^{{hv}/{kT}} - 1}$ Where: - $k$ is the Boltzmann constant 1.38 x 10^-23 J/K - $\nu$ IS THE FREQUENCY OF THE WAVELENGTHS EMITTED (peaks?), REMEMBER - $c$ is the speed of light - $T$ is the **absolute** temperature - $h$ is *planck's constant* - $6.63 \times 10^{-34} J/Hz$ (joules per hertz) See [[Orbitals and Excitations (Chem)|some information of orbitals]] for more! You can click off now if you're a chemistry dude. I still have no idea how Planck did this FYI. ## Extended - A Superposition of Mute Horror and Quantum Mechanics *This kinda fits into quantum mechanics - check out the dedicated doc to learn more! (UNFINISHED)* [[Nuclear & Quantum Contents (Nuclear & Quantum)]]. # Touching on Excitations - *For a more comprehensive rundown on orbitals, check out the dedicated page:* [[Orbitals and Excitations (Chem)]] Although this would belong better in chemistry, it's best for us to talk a little about the fundamentals of our there are **orbitals** in an atom, given with the number $N = 1$ this orbital $N = 1$ is the **ground state** --> the orbital electrons occupy at the start if an electron absorbs a photon it will become excited and jump up an orbital - to orbital $N = 2$ an electron will sometimes reemit a photon taking it back to the ground state --> a photon with the same wavelength as the one they absorbed The further away from the nucleus the harder it is to get to the next orbital in line. # What's Next? You're done with thermal systems! Now for the next logical step - Ideal Gases. To take a first look at Ideal Gases, go here: [[Kinetic Theory & Ideal Gases (Thermodynamics)]] For more relating to excitations, go here: [[Orbitals and Excitations (Chem)]] For more on thermodynamics, go here: [[Thermodynamics - A Contents Page]]