• Rotation of the reflected ray by a mirror: Keeping the incident ray fixed, if the plane mirror is rotated through an angle about an axis in the plane of mirror, then the reflected ray is rotatde through an angle 2.





The glancing angle with M₂ = ( + )



Hence, the new angle of deviation (i.e. COP) = 2( + )



The reflected ray has thus been rotated through BOP when the mirror is rotated through an angle and since



BOP = COP - COB     or     BOP = 2( + ) - 2 = 2 

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