When an object is placed 40 cm away from a spherical mirror an image of magnification 1/2 is produced. To obtain an image with magnification of 1/3, the object is to be moved: (a) 20 cm away from the mirror. (b) 20 cm towards the mirror. (c) 80 cm away from the mirror. (d) 40 cm away from the mirror.

Answer: (d). Erect diminished image, so convex mirror. Use m = f/f-u. u = -40: f/f+40 = 1/2 ⇒ f = 40 cm For m = 1/3: (40)/(40 + x) = 1/3 ⇒ x = 80 cm Object moves from 40 cm to 80 cm. So the answer is (d) 40 cm away from the mirror.

When an object is placed 40 cm away from a spherical mirror an image… | JEE Main 2025 (4 Apr, Shift 1)

Q11JEE Main 2025 · 4 APR · SHIFT 1Medium

Reflection & Mirrors

When an object is placed 40 cm away from a spherical mirror an image of magnification $\frac{1}{2}$ is produced. To obtain an image with magnification of $\frac{1}{3}$ , the object is to be moved:

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Answer: (d)

Erect diminished image, so convex mirror. Use $m = \frac{f}{f-u}$ .
$u = -40$ : $\frac{f}{f+40} = \frac{1}{2} \Rightarrow f = 40\text{ cm}$
For $m = \frac{1}{3}$ : $\frac{40}{40 + x} = \frac{1}{3} \Rightarrow x = 80\text{ cm}$
Object moves from 40 cm to 80 cm. So the answer is (d) 40 cm away from the mirror.

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