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Thermal Properties of Matter
Thermal Radiation and Wien's Law
1 question from 1 paper, each with its answer.
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Concepts tested
- Human body emits infrared
All Questions
2003 AIPMT 1 question
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We consider the radiation emitted by the human body. Which of the following statements is true :Every body above 0 K emits thermal radiation all the time (day and night, summer and winter), and also absorbs radiation from its surroundings.
The wavelength of maximum emission is given by Wien's law, $\lambda_m T = b = 2.9 \times 10^{-3}$ m K.
For the human body, $T \approx 310$ K: $\lambda_m = \dfrac{2.9 \times 10^{-3}}{310} \approx 9.4 \times 10^{-6}$ m $\approx 9.4\ \mu m$
This wavelength lies in the infrared region (longer than visible light, not shorter like ultraviolet). In general, a body at ordinary temperature emits radiation of longer wavelength than the visible and UV radiation it absorbs from sunlight.
So the radiation emitted by the human body is in the infrared region.