Question

Compare the following:
1, Wavelength of the incident solar radiation absorbed by the earth’s surface and the radiation re-radiated by the earth.
2. Tanning effect produced on the skin by UV radiation incident directly on the skin and that coming through the glass window.

Answer 1

Hint: All the wavelengths of light incident on the surface of the earth are first absorbed and converted to heat before re-radiation. Glass can absorb higher wavelengths of the electromagnetic spectrum such as UV rays.

Complete Answer:
We are told to compare.
When solar radiation is incident on the surface of the earth, it would be absorbed. After absorption, all the energy gets converted to heat. From the laws of blackbody radiation, the wavelength of the radiation emitted by the surface of the earth is dependent on the temperature of the earth. Actually, in one of the laws, it says that the peak wavelength is inversely proportional to the temperature. Hence, the earth which is cooler than the sun must emit a longer wavelength.
Also, for the tanning effect,
Generally, the UV radiation is what causes tanning, due to hyper pigmentation on the skin after being absorbed by the skin. In a direct incidence, the tanning effect is maximum, however glass, through glass, it is quite small, and almost negligible. This is because glass, though transparent to visible light, is a very good absorber of UV radiation. In fact, it is almost impossible to get a sunburn from a light passing through glass.

Note: For clarity, the earth being cooler emits a longer wavelength because as said it is inversely proportional to the temperature. But this means that the frequency and thus the energy of the radiation from the earth surface is less than that of the sun. Through this effect, the heat of the heat is kept trapped by being absorbed and reflected by our atmosphere.