The human skin is "selective" when it comes to the absorption of the solar radiation that strikes it perpendicularly. The skin absorbs only 50 percent of the incident radiation with wavelengths between \(\lambda_{1}=0.517 \mu \mathrm{m}\) and \(\lambda_{2}=1.552 \mu \mathrm{m}\). The radiation with wavelengths shorter than \(\lambda_{1}\) and longer than \(\lambda_{2}\) is fully absorbed. The solar surface may be modeled as a blackbody with effective surface temperature of \(5800 \mathrm{~K}\). Calculate the fraction of the incident solar radiation that is absorbed by the human skin.

Short Answer

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Question: Calculate the fraction of the incident solar radiation absorbed by the human skin, given that the skin absorbs 100% of the radiation with wavelengths shorter than 0.517 µm and longer than 1.552 µm, and 50% of the radiation with wavelengths between 0.517 µm and 1.552 µm. The solar surface temperature is 5800 K. Solution: To find the fraction of the absorbed solar radiation, first calculate the energy emitted by the blackbody in the given wavelength range using Planck's radiation formula. Divide this range into three parts: wavelengths shorter than 0.517 µm, wavelengths between 0.517 µm and 1.552 µm, and wavelengths longer than 1.552 µm. Then, calculate the energy absorbed by the human skin by adding the energy absorbed in each wavelength range. Finally, divide the absorbed energy by the total energy emitted by the blackbody, and find the fraction of the absorbed energy.

Step by step solution

01

Calculate the energy emitted per unit wavelength range by the blackbody

For a blackbody, the energy emitted per unit wavelength range (\(E_\lambda\)) is given by Planck's radiation formula: \(E_\lambda (\lambda, T) = \frac{2\pi hc^2}{\lambda^5} \frac{1}{e^{\frac{hc}{\lambda k T}} - 1}\), where \(h\) is Planck's constant, \(c\) is the speed of light, \(k\) is Boltzmann's constant, and \(T\) is the temperature of the blackbody.
02

Calculate the total energy emitted by the blackbody in the wavelength range of interest

To find the total energy emitted by the blackbody in the wavelength range that includes \(\lambda_1\) and \(\lambda_2\), we have to integrate the energy emitted per unit wavelength range with respect to wavelength: \(\int_{0}^{\infty} E_\lambda (\lambda, T) d\lambda = \int_{0}^{\infty} \frac{2\pi hc^2}{\lambda^5} \frac{1}{e^{\frac{hc}{\lambda k T}} - 1} d\lambda\) However, we need to divide the integral into three parts: wavelengths shorter than \(\lambda_1\), wavelengths between \(\lambda_1\) and \(\lambda_2\), and wavelengths longer than \(\lambda_2\). 1) \(E_{\text{short}} = \int_{0}^{\lambda_1} E_\lambda (\lambda, T) d\lambda\)\ 2) \(E_{\text{middle}} = \int_{\lambda_1}^{\lambda_2} E_\lambda (\lambda, T) d\lambda\)\ 3) \(E_{\text{long}} = \int_{\lambda_2}^{\infty} E_\lambda (\lambda, T) d\lambda\)
03

Calculate the energy absorbed by the human skin

Now let's find out the energy that is absorbed by the human skin. As mentioned earlier, 100% of the radiation with wavelengths shorter than \(\lambda_1\) and longer than \(\lambda_2\) is absorbed, while only 50% of the radiation with wavelengths between \(\lambda_1\) and \(\lambda_2\) is absorbed. Therefore, the total absorbed energy is: \(E_{\text{absorbed}} = E_{\text{short}} + 0.5 \times E_{\text{middle}} + E_{\text{long}}\)
04

Calculate the fraction of the absorbed energy

Lastly, we need to find the fraction of the absorbed energy with respect to the total energy emitted by the blackbody. This can be calculated as: \(\text{Fraction of absorbed energy} = \frac{E_{\text{absorbed}}}{E_{\text{total}}}\),\ where \(E_{\text{total}} = E_{\text{short}} + E_{\text{middle}} + E_{\text{long}}\). By calculating the integrals and plugging in all the known values, we can find the fraction of the absorbed energy by the human skin.

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Most popular questions from this chapter

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