Question

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?

Answer 1

Answer:

 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