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?

Question

Denise Beck

Physics

2 May, 12:52

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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Answers (1)

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Izabelle Kirby · Answer 1

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