Help on "Absorption of Radiant Energy by Different Colors"

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KarinaN01
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Joined: Sat Dec 10, 2016 2:50 pm
Occupation: Student

Help on "Absorption of Radiant Energy by Different Colors"

Post by KarinaN01 »

Hello, I am doing the project "Absorption of Radiant Energy by Different Colors". I do not understand how to complete number 7, in the procedures. It states, " Now that you have the data, calculate the energy flow and the energy carried by the visible and infrared photons". I know that I have to use the Stefan-Boltzmann equation, however I do not know what values to plug in. I also need help on the procedures following number 7.

Thanks
stephen_lee
Former Expert
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Joined: Wed Oct 12, 2016 1:40 pm
Occupation: Student

Re: Help on "Absorption of Radiant Energy by Different Colors"

Post by stephen_lee »

Hi KarinaN01,

So for this project when you calculate power using the Stefan-Boltzmann equation, you are calculating power in Watts (P in the equation) using the constant sigma (5.67 × 10-8 W/m2K4), the area of your construction paper squares (A in the equation), and temperature which you'll have to measure (T^4 in the equation). Once you plug in all of these values you will have calculated power.

When using equation 2, you factor in the surrounding temperature (Ts), which will be the temperature of the white background paper.

Now use the power that you calculated to find the amount of photons emitted per second. This can be found by some dimensional analysis. A watt is defined as 1 joule/second, so you can used the power you calculated in watts and rewrite it in joules/second. Then convert the joules to electron volts (eV), where 1 electron volt =1.6 × 10-19 J. Now convert the electron volts to photons using the conversion factor (1photon/0.000124 eV). Now you will get an answer in photons/second for step 8b. All of this information can be found in equation 5 for reference, just make sure that all of your units cancel out except for the photons and seconds which you want to keep for your final answer.

Now for 8c, just compare the calculated results you had from 8a with the Stefan-Boltzmann equation between all of the different color groups. Then compare all of the color groups for photons/second that you calculated in 8b.

Finally, the last steps (9-12) just want you to graph all of your data that you have already collected (temperature readings) or calculated (power from 8a or photons/second from 8b).

Regarding step 7, I'm pretty sure it's just telling you to calculate the power and joules that you will calculate in step 8. There is also a chart in the background section that talks about the different energies of the photons.

If you have any other questions regarding this process feel free to ask me, my name is Stephen.

Good luck with your project!
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