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NDA 2025
Exam
NDA
Year
2025
Subject
General Ability
Chapter
General Science

NDA 2025 · General Ability · General Science

An object is placed between infinity and the pole (P) of a convex...

An object is placed between infinity and the pole (P) of a convex mirror. The position of the image is

Options

  1. Abetween pole (P) and the focus (F), behind the mirror
  2. Bbetween the focus (F) and infinity, behind the mirror
  3. Cbetween the pole (P) and the infinity, in front of the mirror
  4. Dat the focus (F), behind the mirror

Correct answer

A. between pole (P) and the focus (F), behind the mirror

Step-by-step solution

Using the mirror formula:

1v+1u=1f\dfrac{1}{v} + \dfrac{1}{u} = \dfrac{1}{f}

1v=1f−1u\dfrac{1}{v} = \dfrac{1}{f} - \dfrac{1}{u}

For a convex mirror, the focal length ff is positive (f>0f > 0). The object is placed in front of the mirror, so the object distance uu is negative (u<0u < 0).

Since f>0f > 0 and u<0u < 0, the term −1u-\dfrac{1}{u} is positive. Therefore, 1v\dfrac{1}{v} is the sum of two positive quantities, which means 1v>1f\dfrac{1}{v} > \dfrac{1}{f}.

This implies that v<fv < f. Also, since 1v>0\dfrac{1}{v} > 0, we have v>0v > 0.

Thus, 0<v<f0 < v < f. The image is formed between the pole (P) and the focus (F), behind the mirror.

Answer: between pole (P) and the focus (F), behind the mirror
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