Consider a source of light like a candle. The light (intensity) spread as the spherical wave . We know the brightness decreases as we move away from the candle. We want to know exactly what is the intensity of the light falling on the unit area at a particular distance from the source. It can be obtained by dividing source's strength by the area of the sphere at that distance. Intensity on the unit area = source's strength / area of the sphere I=S/4𝚷R² R-Distance from source I proportional 1/R² sin...
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