Solar Energy Q: Mass of Sun Decrease/s?

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Discussion Overview

The discussion revolves around the question of how much the mass of the Sun decreases per second due to the solar energy reaching Earth, specifically considering the energy flux of approximately 1.4 kW per square meter. The scope includes conceptual understanding and mathematical reasoning related to energy and mass conversion.

Discussion Character

  • Exploratory
  • Mathematical reasoning

Main Points Raised

  • One participant suggests calculating the surface area of a sphere with the radius of Earth's orbit and multiplying it by the solar energy flux to determine the total power output of the Sun, followed by applying E=mc² to find the mass decrease.
  • Another participant questions whether the original post is a homework question and suggests it may have been posted inappropriately.
  • A participant clarifies that they are self-studying modern physics, indicating that the inquiry is not for homework purposes.
  • Further elaboration is provided on the method of calculating total power output, emphasizing the assumption of constant flux in all directions and the relationship between power, energy, and time.
  • A participant expresses gratitude for the explanations and shares their interest in physics, while also noting difficulties in initiating problem-solving.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the nature of the original question, with some viewing it as a homework problem while others assert it is a self-study inquiry. The discussion remains unresolved regarding the implications of the calculations suggested.

Contextual Notes

The discussion assumes isotropic distribution of energy and constant flux, but these assumptions are not explicitly confirmed by all participants. There are also unresolved steps in the mathematical reasoning presented.

asdf1
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In this question,
"Solar energy reached the Earth at the rate of about 1.4 kW per square meter of surface perpendictular to the direction of the sun. By how much odes the mass of the sun decrease per second owing to this energy law?"

What is your first reaction to this question? How would you make the first move?
 
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First find the surface area of a sphere with the radius of the Earth's orbit. Multiply by that 1.4kW flux and you'll get the total power output of the sun. Then, apply E=mc^2...
 
What is your first reaction to this question?
That it's a homework question, and has been posted in the wrong part of PF?
 
it's not homework~
i'm trying to self-study modern physics...
 
russ_watters said:
First find the surface area of a sphere with the radius of the Earth's orbit. Multiply by that 1.4kW flux and you'll get the total power output of the sun. Then, apply E=mc^2...

@@a
how did you think of why to "analyze it" that way?
 
asdf1 said:
@@a
how did you think of why to "analyze it" that way?
The question posed - a power flux - 1.4 kW per square meter of surface.

So to get the total power (in kW), one simply multiplies the flux (energy/unit area) by the total area, as Russ indicated. This application assumes that the flux is constant in all directions.

Conversely, to get the flux at some distance, simply divide the total power (again assuming the energy is isotropically distributed) by the area of a sphere at that distance (radius of the sphere).

Remember power = energy per unit time.
 
thank you very much! :)
i think physics is interesting, but i often have trouble making the first step...
thanks so much for explaining!
 

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