Department of Pre-University Education, KarnatakaPUC Karnataka Science Class 12

Light is Incident Normally on a Small Plane Surface. If the Surface is Rotated by an Angle of 30° About the Incident Light, Does the Illuminance of the Surface Increase, Decreases Or Remain Same? - Physics

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Short Note

Light is incident normally on a small plane surface. If the surface is rotated by an angle of 30° about the incident light, does the illuminance of the surface increase, decreases or remain same? Does your answer change if the light did not fall normally on the surface?

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If the surface is rotated by 30°, the illuminance will decrease. This is because illuminance depends upon the cosine of the normal angle.

Yes, if the light does not fall normally on the surface initially, it may increase or decrease depending upon the former's angle. If the 30° rotation brings the table closer to the normal of the surface, the illuminance will increase; otherwise, it will decrease.

Concept: Light Process and Photometry
  Is there an error in this question or solution?


HC Verma Class 11, Class 12 Concepts of Physics Vol. 1
Chapter 22 Photometry
Short Answers | Q 3 | Page 453

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