Blackbody Radiation of Boiling Water

[stanli121]

I was thinking about this the other day and I wanted some other input on the matter. Cups of boiling water (I was thinking about coffee) give off gobs of IR radiation at both near and mid wavelengths. Could I think of a coffee mug as an approximate black body for IR radiation? The insulation of the mug seems to make it possible but I'm really unsure.

Second, is there a decent theoretical manner to calculating the expected peak emissions of hot coffee in a coffee mug? I'm getting very curious and I could always use an IR spectrometer but I was wondering if there's any method via QM based on vibrational modes of water at a given temperature to predict the peak emissions? If the cup can be modeled as a blackbody Planck's Radiation Law solves my problems but I have a hunch it won't be that simple.

Lastly, my understanding of this physics is at the advanced undergraduate level so I should be able to understand any math/theory people throw out for this. Thanks a lot in advance mates!

 

[maverick_starstrider]

I was thinking about this the other day and I wanted some other input on the matter. Cups of boiling water (I was thinking about coffee) give off gobs of IR radiation at both near and mid wavelengths. Could I think of a coffee mug as an approximate black body for IR radiation? The insulation of the mug seems to make it possible but I'm really unsure.

Second, is there a decent theoretical manner to calculating the expected peak emissions of hot coffee in a coffee mug? I'm getting very curious and I could always use an IR spectrometer but I was wondering if there's any method via QM based on vibrational modes of water at a given temperature to predict the peak emissions? If the cup can be modeled as a blackbody Planck's Radiation Law solves my problems but I have a hunch it won't be that simple.

Lastly, my understanding of this physics is at the advanced undergraduate level so I should be able to understand any math/theory people throw out for this. Thanks a lot in advance mates!

I don't understand why you wouldn't expect Wien's Law to give the correct answer?

 

[stanli121]

Doesn't the Wien Law rely on the object being a black body? If the coffee could be considered a black body then this would be a relatively simple thing to figure out but that's where I'm stuck -- whether or not this can be accurately modeled as a black body!

 

[maverick_starstrider]

Doesn't the Wien Law rely on the object being a black body? If the coffee could be considered a black body then this would be a relatively simple thing to figure out but that's where I'm stuck -- whether or not this can be accurately modeled as a black body!

Why wouldn't it be a black body? It's going to have additional absorption/emission depending on the chemistry but it'll still have the black body as the dominant emission. If you don't want to worry about additional emissions then do your experiment in a dark box+faraday cage