Hello. I am trying to study "Introduction to Cosmology" by Barbara Ryden,(adsbygoogle = window.adsbygoogle || []).push({});

but I am stuck with an equation from chapter two, and I have no idea how to figure out this. If you can suggest me a reading material or can explain the equation to me, that would be wonderful.

It is page 20 of the book, chapter 2, equation # 25.

It says:

The energy density of photons in the frequency range f -> f + df is given by the blackbody function

ε(f) df = ((8*∏*h)/(c^3)) ((f^3 * df)/(exp(hf/kT) -1))

and what is that exp?

then it goes...

The peak in the blackbody function occurs at hf_peak =(approx) 2.82kT. Integrated over all frequencies, equation #25 yields a total energy density for blackbody radiation of

ε_γ = α * T^4, ( I wrote "_" to mean subscript).

where

α = ((∏^2)/(15))((k^4)(h^3 * c^3)) <this h is actually h with the dash

the definition of 'α' and the equation#25 just came out of nowhere, and I am very clueless.

And they don't look anything like the blackbody equation that I know:

P_rad = σεAT^4 where ε is emissivity and σ is the Stefan-Boltzmann constant.

Thank you for your help..

Sincerely,

Kyle Lee

**Physics Forums - The Fusion of Science and Community**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Blackbody radiation

Loading...

Similar Threads for Blackbody radiation | Date |
---|---|

I Has cosmic background radiation been measured underground? | Apr 6, 2018 |

I Hawking radiation from de Sitter horizon | Aug 18, 2017 |

Insights A Poor Man's CMB Primer. Part 2: Bumps on a Blackbody - Comments | Oct 5, 2015 |

CMBR as blackbody | Jul 9, 2010 |

Cosmological geometries that may function as blackbodies | Jan 10, 2007 |

**Physics Forums - The Fusion of Science and Community**