what is meaning of geometrical shadow???

A geometrical shadow is the set of points, where drawing a line between points on the shadow and the source always in the line intersecting the corresponding point on the object (obstacle) , or the shadow of the object without any diffraction at the corners.

Let AB be an obstacle towards a source of light. So the area ABC is a geometrical shadow because if we consider a point P on the region ABC and try to draw a line to the source of light, we must intersect AB the obstacle.

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