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By Wien's displacement law the peak emission wavelength of a blackbody is inversely proportional to its absolute temperature. Taking the Sun as a blackbody at 6000 K with its peak in the visible (about 500 nm), estimate the peak wavelength of radiation from a human body treated as a blackbody.

1. 10 nm
2. 10 micrometre
3. 10 mm
4. 10 m

Correct answer: 10 micrometre

Solution

Scaling the Sun's peak by the temperature ratio (6000/300 = 20) gives about 500 nm * 20 = 10 micrometre, in the infrared.

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