Which one of the following materials *cannot* be used to make a convex

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

[amp_mcq option1=”Aluminium” option2=”Glass” option3=”Sapphire” option4=”Water” correct=”option1″]

This question was previously asked in

UPSC CAPF – 2022

The correct answer is A, Aluminium.

A lens works by refracting (bending) light as it passes through the material. For a material to be used to make a lens, it must be transparent or at least translucent to the type of light intended to be used (e.g., visible light for optical lenses).
Glass, Sapphire, and Water are all transparent or translucent materials that can refract light, making them suitable for manufacturing lenses.
Aluminium is a metal that is opaque to visible light. Light does not pass through it but is reflected or absorbed. Therefore, Aluminium cannot be used to make a convex lens for visible light.

Lenses are typically made from materials like glass, plastic, quartz, sapphire, fluorite, or even liquids like water. The choice of material depends on the desired optical properties (like refractive index, dispersion), cost, durability, and the specific wavelength range of light for which the lens is intended.

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