A sunbeam with intensity 10 watts/m ^ 2 is directed perpendicular to a circular window with radius 9.4 meters. What is the power flux of the beam through the window?
The area of the window is `pi ( 9.4 m) ^ 2 = 277.4 m ^ 2, so the flux of a perpendicular 10 watt/m ^ 2 beam will be
The power flux of an energy intensity `intensity (typically measured in Watts/square meter) intercepted at a perpendicular by an area A is simply