A luminous object is placed at a distance of 30 cm from the convex… | NEET 1998 (AIPMT)

Q81NEET 1998 · AIPMTMedium

Combination of Lenses

A luminous object is placed at a distance of $30\text{ cm}$ from the convex lens of focal length $20\text{ cm}$ . On the other side of the lens, at what distance from the lens, a convex mirror of radius of curvature $10\text{ cm}$ , be placed in order to have an upright image of the object coincident with it?

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Answer: (c)

Lens: $u = -30$ , $f = 20$ : $\frac{1}{v} = \frac{1}{20} - \frac{1}{30} \Rightarrow v = 60\text{ cm}$ .
For the image to coincide with the object, rays must hit the convex mirror normally, i.e. head toward its centre of curvature.
So the centre of curvature is at the 60 cm point: mirror distance $= 60 - R = 60 - 10 = 50\text{ cm}$ .
So the answer is (c) $50\text{ cm}$ .

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Combination of Lenses question from NEET 1998 (AIPMT)

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