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### Example 1.3 in the textbook

Posted: **Sun Apr 15, 2018 8:11 pm**

by **Leslie Contreras 1D**

We were only shown Weins law but will we use Stefan-Boltzmann

law Total intensity=constant xT^4

When will this concept come up? Can someone explain to me why T^4

### Re: Example 1.3 in the textbook

Posted: **Sun Apr 15, 2018 9:20 pm**

by **jadam_1E**

I think there will be some concept based questions on stefan boltzmann law, at the very least.

For the second part of your question, T^4 because it was found that the intensity is not simply directly proportional to T, but it is proportional to T^4 (the temperature to the 4th power). The unit used for temperature in the stefan boltzmann law is generally the Kelvin.

### Re: Example 1.3 in the textbook

Posted: **Sun Apr 15, 2018 9:34 pm**

by **Steve H**

An example question: What equation helps astronomers determine a star's temperature, size, composition, and age of a star? Because this concept is new to us and very complex, I am sure there will not be many questions about this on the final/midterm.

### Re: Example 1.3 in the textbook

Posted: **Sun Apr 15, 2018 10:44 pm**

by **Chem_Mod**

There is a physical reason why it should be T^4 which becomes apparent as you start deriving it. However, I will not explain it here since you need to understand statistical mechanics, which you start encountering in upper division physics courses.