Blackbody Radiation of Boiling Water

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SUMMARY

The discussion centers on the blackbody radiation characteristics of boiling water in a coffee mug, questioning whether the mug can be modeled as a black body for infrared (IR) radiation. Participants suggest that while the coffee may not perfectly fit the black body model due to additional absorption and emission properties, it can still be approximated as such for practical calculations. Theoretical approaches, including Planck's Radiation Law and Wien's Law, are highlighted as methods for predicting peak emissions, although the complexities of vibrational modes of water at specific temperatures are acknowledged. The conversation emphasizes the need for controlled experimental conditions to minimize external influences on the measurements.

PREREQUISITES
  • Understanding of Planck's Radiation Law
  • Familiarity with Wien's Law and its application to blackbody radiation
  • Knowledge of quantum mechanics, particularly vibrational modes of molecules
  • Experience with infrared spectroscopy techniques
NEXT STEPS
  • Research the application of Planck's Radiation Law to non-ideal black bodies
  • Explore the principles of Wien's Law in the context of real-world materials
  • Investigate the vibrational modes of water and their impact on IR emissions
  • Learn about experimental setups for measuring IR radiation in controlled environments
USEFUL FOR

Physics students, researchers in thermodynamics, and anyone interested in the infrared properties of liquids and materials, particularly in the context of blackbody radiation.

stanli121
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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!
 
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stanli121 said:
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?
 
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!
 
stanli121 said:
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
 

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