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An incident ray strikes a plane mirror at an angle of incidence of 50°. What is the decrease in the angle of reflection, if the incident ray moves to angle of incidence of 30°?  

An incident ray strikes a plane mirror at an angle of incidence of 50°. What is the decrease in the angle of reflection, if the incident ray moves to angle of incidence of 30°?   Correct Answer 20°

CONCEPT

  • Reflection: The phenomena in which a light ray is sent back into the same medium from which it is coming, on interaction with boundary, is called reflection.
  • Laws of reflection:
  • The angle of incidence (θ i ) = Angle of reflection (θ r )
  • The incident ray, the reflected ray, and normal to the surface of incidence always lies in the same plane.

EXPLANATION:

Given - Initial angle of incidence (i1) = 50° and new angle of incidence (i2) = 30°

  • Therefore, the change in the angle of incidence is

⇒ i = i2 - i1 = 50° - 30° = 20°

  • According to laws of reflection, the angle of incidence = angle of reflection, therefore  

⇒ ∠i = ∠r = 20°

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