Which one of the following materials cannot be used to make a lens ?

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Water

Glass

Plastic

Clay

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Answer is Wrong!

This question was previously asked in

UPSC CISF-AC-EXE – 2022

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A lens is an optical device that transmits and refracts light, causing the convergence or divergence of light rays. For a material to be used to make a lens, it must be transparent or at least translucent enough to allow light to pass through it and must have a refractive index different from the surrounding medium (usually air) so that refraction occurs.
Let’s examine the given options:
A) Water: Water is transparent and has a refractive index. Lenses can be made from water (e.g., water-filled lenses) or exist naturally (e.g., a droplet of water can act as a lens).
B) Glass: Glass is a common, transparent material with a suitable refractive index used extensively for making lenses.
C) Plastic: Many types of plastic are transparent and are widely used for making lenses, especially in eyeglasses, contact lenses, and camera lenses.
D) Clay: Clay is typically opaque (does not allow light to pass through) and therefore cannot be used to make a functional lens that refracts light in the required manner. While it can be molded, its opaqueness makes it unsuitable for transmitting images.

– A lens works by refracting light, which requires the material to be transparent or translucent.
– The material must have a different refractive index from the surrounding medium.
– Opaque materials cannot be used to make standard lenses.

Materials like glass and plastic are commonly used because they are transparent, can be precisely shaped, and have stable optical properties. Water’s shape changes easily, making it less practical for stable lenses unless contained. Clay’s opaqueness fundamentally prevents it from being used for light transmission and refraction in the way a lens operates.

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