(1a). Black body has emissivity value of 1, but in reality, the emissivity of real objects is less than 1. Why?e (1b). The tungsten sphere of 240 mm radius is at a temperature of 25°C. If the power radiated by sphere is 91 W, calculate its emissivity value? (1c).lf the same sphere is enclosed in room whose walls are kept at -7°C, what is the net flow rate of energy out of the sphere in Watts (W)

(1a). Black body has emissivity value of 1, but in reality, the emissivity of real objects is less than 1. Why?e (1b). The tungsten sphere of 240 mm radius is at a temperature of 25°C. If the power radiated by sphere is 91 W, calculate its emissivity value? (1c).lf the same sphere is enclosed in room whose walls are kept at -7°C, what is the net flow rate of energy out of the sphere in Watts (W)

College Physics

1st Edition

ISBN:9781938168000

Author:Paul Peter Urone, Roger Hinrichs

Publisher:Paul Peter Urone, Roger Hinrichs

Chapter14: Heat And Heat Transfer Methods

Section: Chapter Questions

Problem 62PE: The Sun radiates like a perfect black body with an emissivity of exactly 1. (a) Calculate the...

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2.a. What is the total Power emitted (in the form of electromagnetic radiation) by a solid hemisphere of emissivity, e = 1, if its radius is 0.70m, and it is maintained at a temperature of 1280 K ? 2.b. What is the total energy emitted by this object in 90 seconds?
At midday when a large construction site covered with black tarps is directly under the Sun, it receives 975 W of solar power per square meter of surface from the Sun. If this hot surface loses energy only by radiation back into the atmosphere, what is its equilibrium temperature (in K)? You may use an emissivity of e = 1 for a black surface.
Q4: If the power radiated per square centimetre from the skin is equal 0.05 w\ m? fluid the skin temperature? * 320 k°. О з3о 330 k°. О з06 k°. O 400k°.
(1a). Black body has emissivity value of 1, but in reality, the emissivity of real objects is less than 1. Why?? (1b). The tungsten sphere of 220 mm radius is at a temperature of 29°C. If the power radiated by sphere is 105 W, calculate its emissivity value? (1c).If the same sphere is enclosed in room whose walls are kept at -9°C, what is the net flow rate of energy out of the sphere in Watts (W)
The next four questions use this description. Our Sun has a peak emission wavelength of about 500 nm and a radius of about 700,000 km. Your dark-adapted eye has a pupil diameter of about 7 mm and can detect light intensity down to about 1.5 x 10-11 W/m2. Assume the emissivity of the Sun is equal to 1. First, given these numbers, what is the surface temperature of the Sun in Kelvin to 3 significant digits? What is the power output of the Sun in moles of watts? (in other words, take the number of watts and divide it by Avogadro's number) Assuming that all of the Sun's power is given off as 500 nm photons*, how many photons are given off by the Sun every second? Report your answer to the nearest power of 10 (e.g. if you got 7 x 1024, give your answer as 25).
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