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Question
The inverse square law of intensity \[\left(\text{i.e. the intensity }\infty \frac{1}{r^2}\right)\] is valid for a ____________ .
Options
point source
line source
plane source
cylindrical source
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Solution
point source
Intensity of a point source obeys the inverse square law.
Intensity of light at distance r from the point source is given by
\[I = S/\left( 4 \pi r^2 \right)\]
where S is the source strength.
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