Q 12-09-042JEE MainJEE Main 2026 (6 Apr, Shift 2)Easy
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 value type. Enter your answer.
Answer: 10
$m = \dfrac{f}{f - u}$ with $f = -10$ cm.
Real image ($m = -2$): $-2 = \dfrac{-10}{-10 - u} \Rightarrow u = -15$ cm.
Virtual image ($m = +2$): $2 = \dfrac{-10}{-10 - u} \Rightarrow u = -5$ cm.
Distance between the positions $= 15 - 5 = 10$ cm.
Solution by Sreeraj P, M.Sc Physics