Q.A student uses spectacles of number -2 for seeing distant objects. Commonly used lenses for her/his spectacles are (A) bi-concave (B) double concave (C) concavo-convex (D) convexo-concave

[!TLDR] A negative spectacle number is a diverging correction, and the book states convexo-concave lenses are the common shape used for …

Spectacle 'number' equals focal power in dioptres; a NEGATIVE number (like -2) means a diverging (concave-acting) correction, used for myopia (short-sightedness, for seeing distant objects clearly). The chapter states directly that concavo-convex and convexo-concave (meniscus) lenses are the shapes commonly used for spectacles of positive and negative number respectively -- so a negative-number lens is convexo-concave (net diverging, despite having one convex face, because the concave face's curvature dominates). Plain bi-concave or double-concave lenses, while also diverging, a …

Recall that spectacle 'number' is the focal power in dioptres, with sign indicating converging (positive, hypermetropia correction) or diverging (negative, myopia correction), then m …

Choosing a plain bi-concave/double-concave option, missing that spectacles use the meniscus (concavo-convex family) shapes ra …