Fundamentholfundamenthol
JEE Main2026Jan 22, Shift 2Physics
Q.

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

  1. A

    between the focus (F) and the centre of curvature (C) of the mirror ONLY

  2. B

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

  3. C

    beyond the centre of curvature (C) of the mirror ONLY

  4. D

    between the pole (P) and the focus (F) of the concave mirror ONLY

Solution

For the parallax method, the image must be real and inverted so that it can be compared with an external reference pin.

A concave mirror gives a real image only when the object lies beyond the focal point (i.e., distance from mirror greater than ). Hence the object should be placed at any point beyond F.

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