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8 September, 05:39

A python can detect thermal radiation from objects that differ in temperature from their environment as long as the received intensity of thermal radiation is greater than 0.60 W/m2. Your body emits a good deal of thermal radiation. Assume that your body has a surface area of 1.6 m2, a surface temperature of 30°C, and an emissivity e = 0.97 at infrared wavelengths. As we've seen, the intensity of a source of radiation decreases with the distance from the source. If you are outside on a cool, dark night, what is the maximum distance from which a python could detect your presence?

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  1. 8 September, 06:22
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    R = 9.92 m

    Explanation:

    For this exercise let's use the Stefa radiation equation

    P = σ A e T⁴

    Where the Stefan-Boltzmann constant is worth 5,670 10⁻⁸ W/m²K⁴, A is the area of the body and the emissivity and T is the absolute temperature

    Let's calculate irradiated

    P = 5,670 10⁻⁸ 1.6 0.97 (273 + 30) 4

    P = 7.417 10² W

    The emitted power is distributed on a spherical surface as it progresses, whereby the intensity detected by the python I = 0.6 W / m2

    P = I A

    The area of the sphere is

    A = 4π R²

    P = I 4π R²

    R² = P / 4π I

    R = √ [7.417 102 / (4π 0.6) ]

    R = √ 98.37

    R = 9.92 m
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