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Ray Optics and Optical Instruments

  1. A beam of light from a source L is incident normally on a plane mirror fixed at a certain distance x from the source. The beam is reflected back as a spot on a scale placed just above the source I. When the mirror is rotated through a small angle θ, the spot of the light is found to move through a distance y on the scale. The angle θ is given by
    1. y
      x
    2. x
      2y
    3. x
      y
    4. y
      2x
Correct Option: D

When mirror is rotated by  angle θ reflected ray will be rotated by 2θ.

y
= 2θ ⇒ θ =
y
x2x



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