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JEE Main 2023 (25 Jan, Shift 2) · Combination of Lenses

Combination of Lenses question from JEE Main 2023 (25 Jan, Shift 2)

Q39JEE Main 2023 · 25 JAN · SHIFT 2Medium

Combination of Lenses

An object is placed on the principal axis of convex lens of focal length 10cm as shown. A plane mirror is placed on the other side of lens at a distance of 20 cm. The image produced by the plane mirror is 5cm inside the mirror. The distance of the object from the lens is ___________ cm.

Figure

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

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Answer: 30

  1. Plane mirror image is 5 cm behind it, so the lens image (mirror's object) is 5 cm in front of the mirror: v=20−5=15 cmv = 20 - 5 = 15\text{ cm} from the lens.
  2. Lens formula: 1u=1v−1f=115−110=−130\frac{1}{u} = \frac{1}{v} - \frac{1}{f} = \frac{1}{15} - \frac{1}{10} = -\frac{1}{30}
  3. So the object is 30 cm from the lens.
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