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Wize University Physics Textbook (Master) > Heat and Temperature

Heat Transfer: Black Body Spectrum

Heat Transfer: Solar SystemPrevious Section
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Radiation Spectrum and Wien's Law


Wein's Law relates the peak wavelength of black body radiation to the absolute temperature. Wein's law states:
λmax⁡T=2.898×10−3[mK]\boxed{\hspace{2.3cm}\lambda_{\max}T=2.898\times10^{-3}[mK]\hspace{2.3cm}}

Thermal radiation is more properly called electromagnetic radiation and spans the whole EM spectrum. Most of the thermal energy transferred is in the infrared side of the light spectrum. Metal will glow in the red/orange and be producing visible light, but most of the energy transfer will be through in sub-red wavelengths.

Extra Practice
New Practice Question
The power of radiation light bulb A is double the power of radiation of light bulb B. Both bulbs are in spherical shape but the radius of bulb B is double the radius of bulb A. If they have the same emissivity factor, find a relationship between the wavelength at which these bulbs have their max power radiated.
New Practice Question
A solar panel is made of 6 rectangular sections each with dimensions of 1.8m by 2m. The albedo factor of this panel is calculated to be 0.4 and it has the emissivity factor of 0.8. This panel is 24% efficient in converting light to electrical power. If the solar constant on earth is 1360 W/m2:
a) Find the power produced by this panel when it is exposed to the Sun.
b) Find the temperature of the panel when it is exposed to the Sun.
Electromagnetic radiation: Wave energy
Given a hot stone (T=1400°CT=1400\degree C), what is the peak wavelength of radiation? Where is this compared to the visible spectrum? Can you use this principle to describe why an object may not look hot, but actually be emitting large amounts of energy?