(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 290 mm radius is at a temperature of 31°C. If the power radiated by sphere is 93 W, calculate its emissivity value? (1c).If 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?? (1b). The tungsten sphere of 290 mm radius is at a temperature of 31°C. If the power radiated by sphere is 93 W, calculate its emissivity value? (1c).If 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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The Sun radiates like a perfect black body with an emissivity of exactly 1. (a) Calculate the surface temperature of the Sun, given that it is a sphere with a 7.00108m radius that radiates 3.801026W into 3-K space. (b) How much power does the Sun radiate per square meter of its surface? (c) How much power in watts per square meter is that value at the distance of Earth, 1.501011m away? (This number is called the solar constant.)
One way to cool a gas is to let it expand. When a certain gas under a pressure of 5.00 106 Ha at 25.0C is allowed to expand to 3.00 times its original volume, its final pressure is 1.07 106 Pa. (a) What is the initial temperature of the gas in Kelvin? (b) What is the final temperature of the system? (See Section 10.4.)
A 1.00MT bomb exploded a few kilometers above the ground deposits 25.0% of its energy into radiant heat. (a) Find the calories per cm2 at a distance of 10.0 km by assuming a uniform distribution over a spherical surface at that radius. (b) If this heat falls on a person’s body, what temperature increase does it cause in the affected tissue, assuming it is absorbed in a layer 1.00cm deep?
(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).If 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)
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4G lI. Aa lag question (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 260 mm radius is at a temperature of 33°C. If the power radiated by sphere is 89 W, calculate its emissivity value? (1c).lf the same sphere is enclosed in room whose walls are kept at -19°C, what is the net flow rate of energy out of the sphere in Watts (W) Your story Close Friends
A super-insulated house is at a temperature of 20°C. The temperature outside is 0°C. The surface area of the house is 200 m², and the emissivity is 1. Approximately how much energy is radiated (in W) per second? a. 20 000 b. 20 000 с. 200 d. O b a
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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Q10: In a nuclear reactor, 1-cm-diameter cylindrical uranium rods cooled by water from outside serve as the fuel. Heat is generated uniformly in the rods (k = 29.5 W/m - °C) at a rate of 7 x10 w/m?. If the outer surface temperature of rods is 175°C, determine the temperature at their center. Q11: Consider a homogeneous spherical piece of radioactive material of radius ro =0.04 m that is generating heat at a constant rate of g'= 4 x 10' w/m. The heat generated is dissipated to the environment steadily. The outer surface of the sphere is maintained at a uniform temperature of 80°C and the thermal conductivity of the sphere is k = 15 W/m "C. Assuming steady one-dimensional heat transfer, (a) express the differential equation and the boundary conditions for heat conduction through the sphere, (b) obtain a relation for the variation of temperature in the sphere by solving the differential equation, and (c) determine the temperature at the center of the sphere. Q12: Consider a large…
Q1: A 1.5mx0.8m double glass window consists of two glass(k=0.78 W/mC) layers with a 4 mm thickness for each layer, seperated by a 10 mm thick of still air gap. If the thermal cnductivity of still air is 0.026 W/mC, what is the rate of heat transfer through the window, if the temperatures of the inner and outer surfaces of the window are 15 and -8°C respectively. يتكون شباك ارتفاعه 0.8m وعرضه 1.5m من طبقتين من الز جـاج 0.78 k=( (°CW/m سمك كل واحدة منهما Am m ومفصولتين بطبقة هوائية سمكها 10mm . إذا كان معامل الانتقال بالتوصيل ل لهواء الساكن W/m °C 0.026 أحسب معدل انتقال الحرارة خلال الشباك إذا كانت درجة حرارة السطح الداخلي ل لشباك C° 15 ودرجة حرارة السطح الخارجي C° 8-. T2 T3 هواء Glass Air Glass Ax, A X, A X3
Heat flux meters use a very sensitive device known as a thermopile to measure the temperature difference across a thin, heat conducting film made of kapton (k = 0.345 W/m - K). If the thermopile can detect temperature differences of 0.1°C or more and the film thickness is2 mm, what is the minimum heat flux this meter can detect?