Question

Figure shows a small diffused plane source S placed over a horizontal table-top at a distance of 2.4 m with its plane parallel to the table-top. The illuminance at the point A directly below the source is 25 lux. Find the illuminance at a point B of the table at a distance of 1.8 m from A.
Figure

Answer 1

Answer:

11.2 Lux

Explanation:

25*2.4^2=144 candela

I = 25*2.4^4 / 3( Pythagorean’s theory)

I = 33.1776 / 3

I = 11.2 lux

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