We're covering flux/luminosity/magnitudes etc in Astrophysics module at the moment but I'm getting myself into a bit of a muddle when it comes to flux.(adsbygoogle = window.adsbygoogle || []).push({});

We've been given monochromatic and bolometric flux equations, both with respect to wavelength and with respect to frequency.

And I'm trying to understand the relationship and conversion between the monochromatic flux wrt wavelength and wrt frequency but finding it quite confusing. It doesn't help that every textbook I look in seems to call it a different name!

Are "monochromatic flux", "spectral flux density" and "flux density" all the same thing? The two texts I'm looking at currently both quote them as the same definition, i.e power divided by area of telescope and the bandwidth. And all quote units of W m^{-2}Hz^{-1}or W m^{-2}nm^{-1}. (Some texts go on to mention angles and derive new quantities but we haven't covered that yet so I'm only looking at the basic form).

The equations we have been given are:

Monochromatic flux wrt frequency,

[tex]F_{\nu} = \frac{\Delta E}{\Delta A\Delta t\Delta\nu}[/tex]

and monochromatic flux wrt wavelength,

[tex]F_{\lambda} = \frac{\Delta E}{\Delta A\Delta t\Delta\lambda}[/tex]

If they are one and the same, why then would one text say that in order to convert between F(lambda) and F(nu) you would use

[tex]\nu F_{\nu} = \lambda F_{\lambda}[/tex] http://books.google.co.uk/books?id=cc9L8QWcZWsC&pg=RA1-PA94&lpg=RA1-PA94"

but others say that you need to use

[tex]F_{\nu} d\nu = -F_{\lambda} d\lambda[/tex] which then goes down to

[tex]F_{\nu} = F_{\lambda} \left(\frac{\lambda^{2}}{c} \right)[/tex] http://books.google.co.uk/books?id=hp7vyaGvhLMC&pg=PA337&lpg=PA337"

Confused! :uhh:

**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!

# Confused about monochromatic flux

Loading...

Similar Threads for Confused monochromatic flux | Date |
---|---|

I Confusion about Corotational and Lindblad resonance | Jan 22, 2018 |

I Some confusion about Kepler’s formula | Jan 10, 2018 |

B Confused about traveling at the speed of light | Dec 20, 2016 |

B Are black holes white or monochromatic? | Dec 19, 2016 |

B The news media on 2 trillion galaxies: Confused, or am I? | Oct 15, 2016 |

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