Max Distance from which a python detects infrared radiation

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SUMMARY

A python can detect thermal radiation with an intensity greater than 0.60 W/m². Given a typical human body with a surface area of 1.8 m², a surface temperature of 30°C, and an emissivity of 0.97, the maximum distance from which a python can detect a human is calculated to be approximately 10.5 meters. This calculation utilizes the Stefan-Boltzmann law and the inverse square law for radiation intensity. The peak wavelength of the emitted radiation is determined to be around 9571 nm, indicating that the majority of the emitted power is in the infrared spectrum.

PREREQUISITES
  • Understanding of thermal radiation concepts
  • Familiarity with the Stefan-Boltzmann law
  • Knowledge of inverse square law for radiation
  • Basic proficiency in physics equations and units
NEXT STEPS
  • Study the Stefan-Boltzmann law in detail
  • Learn about infrared radiation detection methods
  • Explore the physics of emissivity and its applications
  • Investigate the behavior of snakes and their sensory capabilities
USEFUL FOR

Students in physics, wildlife biologists, and anyone interested in the sensory mechanisms of reptiles, particularly in understanding how pythons detect thermal radiation.

Venerable R
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Homework Statement



A python can detect thermal radiation with intensity greater than .60 W/m2. A typical human body has a surface area of 1.8 m2, a surface temperature of 30°C, and an emissivity e=0.97 at infrared wavelengths. What is the maximum distance from which a python can detect your presence? You can model the human body as a point source of radiation.

I = .60 W/m2
e = 0.97
T = 303 K
A = 1.8 m2
d = ? (m)

Homework Equations


[/B]
λ = (2.9*106 nm⋅K)/ Temp (in K)
I = P/(4πr2)
Q/Δt = eσAT4
σ = 5.67 * 10 -8 W/(m2⋅K4)

The Attempt at a Solution



λ = (2.9*106 nm⋅K)/ 303 K = 9571 nm

And if P = Watts, A = m2, and I = W/m2
Then, P = I*A → .60*1.8 = 1.08 W

.60 W/m2 = (0.97 * 1.08 W)/(4πr2)
r = .37 m

Honestly, I'm not sure what else to do. I don't think "P" is correct.
 
Last edited:
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Hello R, welcome to PF :)

I agree P probably isn't correct. Is it clear what the relevant equations you are listing stand for ?
I like the third one: Q/time (aka P !), according to the Stefan-Boltzmann law
You have all the ingredients to evaluate the human body emission ##P_{emit}##. It's rather a lot.
Your first equation tells you the peak wavelength of the intensity distribution spectrum is at over 9000 nm, so most of this P is in the infrared.
I suppose (but don't know for sure -- perhaps someone else can confirm or correct) that fraction is precisely the emissivity factor.

And that is the P you want to distribute over a sphere using your second equation. By the time r is so big that I < 0.6 W/m2 you've found the range.
 
BvU said:
Hello R, welcome to PF :)

I agree P probably isn't correct. Is it clear what the relevant equations you are listing stand for ?
I like the third one: Q/time (aka P !), according to the Stefan-Boltzmann law
You have all the ingredients to evaluate the human body emission ##P_{emit}##. It's rather a lot.
Your first equation tells you the peak wavelength of the intensity distribution spectrum is at over 9000 nm, so most of this P is in the infrared.
I suppose (but don't know for sure -- perhaps someone else can confirm or correct) that fraction is precisely the emissivity factor.

And that is the P you want to distribute over a sphere using your second equation. By the time r is so big that I < 0.6 W/m2 you've found the range.

Oh! So, using P = eσAT4, I found P = 834 W.
Then, I = P/(4πr2), I found that r = 10.5 m!

That's seems realistic! Thank you for all your help! :D
 
I hope it's the right answer...
Tried to check by working it out for a mouse (after all, a much more likely item on the snake menu) of, say, 25 gram, so 1/3500 times the weight and some (1/3500)2/3 the area. About 66 cm, so life isn't all that easy for a snake...

I also think I remember hearing that snakes only 'see' movement.

Oh, well, with physics you can't know everything (although some physicists seem to think otherwise ;) )