Lab+07+_Radiation - Name___________________________________...

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Unformatted text preview: Name___________________________________ Section ___________ EAS 1601 Lab 7 Solar Radiation Sample Prelab Quiz (note: actual quiz may differ) NASA is designing a spacecraft which will pass within a 100,000 km of a star that has a surface temperature of 5000K and a radius of 12,000 km. (Assume the spacecraft is a sphere) Given that the Stephan-Boltzmann Constant = 5.67x10-8 W m-2 K-4 : 1. What will the radiative flux be when the spacecraft is at the distance specified above? (4 pts) 2. Because of various technology and engineering constraints, it is essential that the surface temperature of the spacecraft be kept below 500 K. What must the albedo of the spacecraft be in order to achieve this temperature? (4 pts) 3. How do you convert temperature given in K into degrees Celsius and Fahrenheit? (2 points) 1 Name___________________________________ Section ___________ EAS 1601 Lab 7 Solar Radiation Objective: To investigate the Earth as a blackbody and to study the radiation laws, dependence of energy flux on the distance. At the end of this lab, the student should be able to: Define a perfect blackbody. Understand the Earths energy balance. Calculate the solar flux under experimental conditions. Relate a solar flux and albedo to the Earths effective temperature. Describe and explain the effect that controlling conditions have on Earths effective temperature in the experiment. Background. By energy conservation principle, the net radiative energy gained by arbitrary body in a unit time ( E net ) is defined by difference of incoming ( E in ) and outgoing ( E out ) energy. E net =E in - E out The incoming energy E in due to some distant source depends on energy flux S (the amount of energy passing through unit area perpendicular to the direction of propagation, W/m 2 ) impinging the body, and cross-sectional area A that intercepts this flux: ) 1 ( a S A E in = where a- albedo of the body. Consider the point source radiating total power P at distance R from the body. We can assume that the energy from the point source is evenly distributed over the sphere with radius R and area 4 R 2 , and therefore, the energy flux S will be equal to amount of power passing through a unit area of this sphere 2 4 R P S = . The following equation relates flux S at distance R to the known flux S o at some reference distance R o : S = S o (R o /R) 2 According to Stefan-Boltzmann law blackbodies at the temperature T radiate the electromagnetic energy, and the flux of this energy is equal to S= T 4 , where is the Stephan- 2 Name___________________________________ Section ___________ Boltzmann Constant 5.67x10-8 W m-2 K-4 . Then total outgoing energy of the body equal to radiated flux times total surface area of the body A : E out = ....
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This note was uploaded on 02/08/2011 for the course EAS 1601 taught by Professor Lynch during the Spring '08 term at Georgia Institute of Technology.

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Lab+07+_Radiation - Name___________________________________...

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