Which of the following statements about the law of illumination is correct?

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SSC JE Electrical 15 Nov 2022 Shift 2 Official Paper
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  1. The illumination is directly proportional to the luminous intensity and inversely proportional to the square of distance of the surface from the source.
  2. The illumination is directly proportional to the luminous intensity and inversely proportional to the distance of the surface from the source.
  3. The illumination is directly proportional to the distance of the surface from the source and inversely proportional to the square of luminous intensity.
  4. The illumination is directly proportional to the square luminous intensity and inversely proportional to the distance of the surface from the source.

Answer (Detailed Solution Below)

Option 1 : The illumination is directly proportional to the luminous intensity and inversely proportional to the square of distance of the surface from the source.
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Detailed Solution

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Laws of illumination

1.) Inverse square law

This law states that the illumination at any point on a plane is directly proportional to the luminous intensity and inversely proportional to the square of the distance of the surface from the source.

But the drawback of inverse square law is that this law is only applicable if the light source is considered as a point source.

2.) Lambert's Cosine Law

The law states that illumination at a point on a plane is proportional to the cosine of the angle of light incident and inversely proportional to the square of the distance of the surface from the source.

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