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Math Help - Physics question

  1. #1
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    Physics question

    How can I calculate the intensity of radiation of the Sun at Earth(at the same distance as the Earth is at). The intenisity of radiation at the Sun is about 64MW/m2. I mean the radiation spreads around so how can I know which portion comes to the Earth?



    All help is appreciated.
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  2. #2
    Member Danshader's Avatar
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    well saying that the radiation from the sun all travels at the same speed
    , this radiation will cover a spherical shape of area.(just like blowing a balloon)

    now the distance of the earth to the sun is about 1.5x10^{11}m
    this means you need to find the surface area of a sphere with a radius of 1.5x10^{11}m, then you need to find the area of intersection between the sphere and the earth(assume to be in the middle of the earth)

    surface area of the sphere:
    <br />
A_1 = 4\pi r_{ES}^2<br />
    where r_{ES} ^2 is the radius of the earth and has the value of 1.5x10^{11}

    hence the area of intersection is:
    <br />
A_2 = \pi r _E ^2<br />

    where r_E ^2 is the radius of the earth and has the value of 6.4x10^6. The area of intersection is can be assumed as a circle since the distance of the earth from the sun is very much larger tahn the radius of the earth.

    hence the fraction of radiation received by earth is
    \frac{A_2}{A_1}
    Last edited by Danshader; April 29th 2008 at 07:56 AM.
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