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In parallax method for the determination of focal length of a concave mirror, the object should always be placed:

Options

  1. Abetween the focus (F) and the centre of curvature (C) of the mirror ONLY
  2. Bbetween the pole( P ) and the focus (F) of the concave mirror ONLY
  3. Cbeyond the centre of the curvature (C) of the mirror ONLY
  4. Dat any point beyond the focus (F) of the mirror

Correct answer

D. at any point beyond the focus (F) of the mirror

Step-by-step solution

In the parallax method for determining the focal length of a concave mirror, we use an object pin and its real image formed by the mirror. The method of 'no parallax' involves aligning the tip of the object pin with the tip of its real image. This is only possible if the image formed is real. For a concave mirror, a real image is formed only when the object is placed at any position beyond the focus ( F ), i.e., u > f . If the object is placed between the pole ( P ) and the focus ( F ), the image formed is virtual,

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