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JEE Main · 2023 · 08 Apr 2023 · Shift 1 · Geometrical Optics

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In a reflecting telescope, a secondary mirror is used to:
  1. (A)reduce the problem of mechanical support
  2. (B)remove spherical aberration
  3. (C)make chromatic aberration zero
  4. (D)move the eyepiece outside the telescopic tube✓ Correct

Answer: (D)

Solution

In a reflecting telescope the objective is a large concave mirror at the closed end of the tube, so its focus lies inside the tube where an eyepiece cannot be mounted conveniently. A small secondary mirror intercepts the converging beam and redirects it, either out through a hole in the objective or out through the side of the tube, so that the image is formed in an accessible position. The observer can then view it comfortably from outside the body of the instrument. Hence the secondary mirror is used to move the eyepiece outside the telescopic tube.

JEE Main · 2023 · 08 Apr 2023 · Shift 1 · Single correct option

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