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Praxis II General Science

Category - Physics

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For a black body, Stefan-Boltzmann’s law predicts that radiation is equal to P = σAZ, where σ is 5.7x10^-8W*m^-2*K^-4, also known as Stefan’s constant. A is the area and Z is a constant describing the difference between the black body temperature and that of the surrounding environment. Given this information, Z = 1.5 x 10⁹ and the area of an average human child as 1.0 m², how much radiation energy does a child emit?

50 watts
85 watts
140 watts
251 watts
300 watts

Explanation

Answer: B - A human child would emit about 85 watts of energy. Using the equation, we can plug in the constants given to find that P = 5.7 x 10^-8 * 1.5 x 10⁹ * 1. Canceling out the exponents, the simplified equation is 5.7 x 15 x 1 = 85.5 watts.

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Praxis II General Science

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