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B Irradiance at a point on a surface

  1. Jul 30, 2016 #1
    My book states that "irradiance at a point on the outer sphere is less than irradiance at a point on the inner sphere."


    The formula is simple, it's flux/area. So in case of a sphere its flux/4π*r^2.
    But my question is what exactly does this formula give? does it give the total flux that arrives on a point on the sphere? If so, what are the dimensions of that point? The book totally confused me on that part.
  2. jcsd
  3. Jul 30, 2016 #2


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    Gold Member

    power or flux (energy/time) per area = irradiance
    It gives you how much energy per unit of time passes through some area.
    No point is concerned, except for if around that point you draw an infinitesimal surface. So you can determine its value at those points.
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