How Does a Sphere Exchange Thermal Radiation in Different Temperatures?

In summary: J/s or -79.92 J/s, depending on which way you decide is positiveIn summary, a sphere with a radius of 0.5m, temperature of 27 degrees Celsius, and emissivity of 0.85 is in an environment of 77 degrees Celsius. The rate of thermal radiation emission and absorption can be calculated using the equation P = d(ε)(A)(T^4), where d is the Stefan-Boltzmann constant, ε is the emissivity, A is the surface area, and T is the temperature. For emission, the sphere's temperature should be used, while for absorption, the environment's temperature should be used. The net rate of energy exchange can be
  • #1
bmb2009
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Homework Statement


A sphere of radius .5m, temperature of 27 deg C, and emissivity = .85 is located in an environment of temperature 77 deg C. At what rate does the sphere (a)emit and (b)absorb thermal radiation? (c)What's the sphere's net rate of energy exchange?



Homework Equations





The Attempt at a Solution



(a). I know I must use the equation P = d(ε)(A)(T^4) where d = stefan-Boltz constant, ε= emissivity, A=surface area, T=temperature...but which temperature is it? I believe I should use the Sphere's temp for the emission quantity and the temp of the enviorment for the absorption radiation quantity. Is that correct?

(c) I haven't been given an equation for net rate of energy exchange but wouldn't it just be absorption - emission ?

Thanks for the help!
 
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  • #2
Yes, that all looks right to me. Degrees K, of course.
 
  • #3
bmb2009 said:

Homework Statement


a sphere of radius .5m, temperature of 27 deg c, and emissivity = .85 is located in an environment of temperature 77 deg c. At what rate does the sphere (a)emit and (b)absorb thermal radiation? (c)what's the sphere's net rate of energy exchange?



Homework Equations





The Attempt at a Solution



(a). I know i must use the equation p = d(ε)(a)(t^4) where d = stefan-boltz constant, ε= emissivity, a=surface area, t=temperature...but which temperature is it? I believe i should use the sphere's temp for the emission quantity and the temp of the enviorment for the absorption radiation quantity. Is that correct?

(c) i haven't been given an equation for net rate of energy exchange but wouldn't it just be absorption - emission ?

Thanks for the help!

a-ok.
 

1. What is thermodynamics?

Thermodynamics is the branch of science that deals with the transfer of heat and its relation to other forms of energy, such as work. It also studies how energy is converted from one form to another and how it affects the properties of matter.

2. What are the laws of thermodynamics?

The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or converted from one form to another. The second law states that the total entropy of a closed system will always increase over time, meaning that energy tends to disperse and spread out rather than stay concentrated in one place.

3. What is the difference between heat and temperature?

Heat is a form of energy that is transferred from one object to another due to a difference in temperature. Temperature is a measure of the average kinetic energy of the particles in a substance. In other words, heat is the transfer of energy, while temperature is a measure of the amount of energy in a substance.

4. What is an example of thermodynamics in everyday life?

An example of thermodynamics in everyday life is the operation of a refrigerator. The first law of thermodynamics is demonstrated as the compressor transfers energy from the inside of the refrigerator to the outside, cooling the inside. The second law is demonstrated as the inside of the refrigerator stays cool while the outside warms up, increasing the overall entropy of the system.

5. How is thermodynamics applied in engineering?

Thermodynamics is applied in engineering to design and improve various systems, such as power plants, engines, and refrigeration systems. Engineers use the laws of thermodynamics to optimize the efficiency and performance of these systems, ensuring they operate within the constraints of the laws.

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