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JEE Main 2026 (6 Apr, Shift 2) · Reflection & Mirrors

Reflection & Mirrors question from JEE Main 2026 (6 Apr, Shift 2)

Q3JEE Main 2026 · 6 APR · SHIFT 2Medium

Reflection & Mirrors

A concave mirror of focal length 10 cm forms an image which is double the size of object when the object is placed at two different positions. The distance between the two positions of the object is ______ cm.

Numerical answer type. Work it out, then open the answer.

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Answer: 10

  1. m=ff−um = \frac{f}{f - u} with f=−10 cmf = -10\text{ cm}.
  2. Real image, m=−2m = -2: f−u=−f2⇒u=3f2=−15 cmf - u = -\frac{f}{2} \Rightarrow u = \frac{3f}{2} = -15\text{ cm}
  3. Virtual image, m=+2m = +2: f−u=f2⇒u=f2=−5 cmf - u = \frac{f}{2} \Rightarrow u = \frac{f}{2} = -5\text{ cm}
  4. Distance between the two positions =15−5=10 cm= 15 - 5 = 10\text{ cm}
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