1. the formula for power radiated in the form of electromagnetic energy by an ob

Question

1. the formula for power radiated in the form of electromagnetic energy by an object at nonzero temperature. This formula applies to _______________. a.any object of total surface area A , Kelvin temperature T, and emissivity e b.any object of cross-sectional area A , Kelvin temperature T, and emissivity e c.any object of total surface area A , Kelvin temperature T, and emissivity d.any object of cross-sectional area , Kelvin temperature , and emissivity 2. If you calculate the thermal power radiated by typical objects at room temperature, you will find surprisingly large values, several kilowatts typically. For example, a square box that is 1 on each side and painted black (therefore justifying an emissivity near unity) emits 2.5 Kw at a temperature of 20 C. In reality the net thermal power emitted by such a box must be much smaller than this, or else the box would cool off quite quickly. Which of the following alternatives seems to explain this conundrum best? a.The box is black only in the visible spectrum; in the infrared (where it radiates) it is quite shiny and radiates little power b.The surrounding room is near the temperature of the box and radiates about 2.5 of thermal energy into the box c.Both of the first two factors contribute significantly d. Neither of the first two factors is the explanation 3. As a rough approximation, the human body may be considered to be a cylinder of length L= 2m and circumference C=0.8m . (To simplify things, ignore the circular top and bottom of the cylinder, and just consider the cylindrical sides.) If the emissivity of skin is taken to be e=0.6, and the surface temperature is taken to be T=30C , how much thermal power P does the human body radiate? Express the power radiated numerically; give your answer to the nearest 10 .

Explanation / Answer

Part D As a rough approximation, the human body may be considered to be a cylinder of length L=2.0m and circumference C=0.8m. (To simplify things, ignore the circular top and bottom of the cylinder, and just consider the cylindrical sides.) If the emissivity of skin is taken to be e=0.6, and the surface temperature is taken to be T=30?C, how much thermal power P does the human body radiate? Express the power radiated numerically; give your answer to the nearest 10 W. P = 460 W SubmitHintsMy AnswersGive UpReview Part Correct Part D As a rough approximation, the human body may be considered to be a cylinder of length L=2.0m and circumference C=0.8m. (To simplify things, ignore the circular top and bottom of the cylinder, and just consider the cylindrical sides.) If the emissivity of skin is taken to be e=0.6, and the surface temperature is taken to be T=30?C, how much thermal power P does the human body radiate? Express the power radiated numerically; give your answer to the nearest 10 W. P = 460 W SubmitHintsMy AnswersGive UpReview Part Correct P = 460 W P = 460 W SubmitHintsMy AnswersGive UpReview Part Correct Correct Correct P = 460 W

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