JEE Main · 2026 · 06 Apr 2026 · Shift 2 · Geometrical Optics

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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.

Answer: 10

Solution

A magnification of magnitude

2

occurs at two object positions. For the real, inverted image

m = - \frac{v}{u} = - 2

gives

v = 2 u

; with

f = - 10 cm

\frac{1}{2 u} + \frac{1}{u} = - \frac{1}{10}

yields

u = - 15 cm

. For the virtual, erect image

m = + 2

gives

v = - 2 u

, and

\frac{1}{- 2 u} + \frac{1}{u} = - \frac{1}{10}

yields

u = - 5 cm

. The object stands

15 cm

and

5 cm

from the mirror, a separation of

10 cm

JEE Main · 2026 · 06 Apr 2026 · Shift 2 · Integer answer

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