Question

Give reasons: A concave lens is used to correct myopia.

Answer 1

Hint: There are eye disorders seen in humans. In these disorders, instead of light focusing on the retina, focus either in front of the retina or at the back of it. Due to this refractive error, in which the eye cannot focus light properly on the retina, vision gets blurred. It can be due to genetic or environmental factors. To correct these disorders, either converging or diverging lenses are used.

Complete answer:
There are different types of eye disorders such as Myopia, Hypermetropia, Presbyopia and Astigmatism.
Myopia is an eye disorder in which the light focuses in front of the retina instead of focussing on the retina. In this find of disorder, the distant objects appear blurred while the objects near to us appear normal. It is also known as Near-sightedness or short-sightedness. To correct this problem, the lens must be weakened. Thus, to weaken the lens concave lenses are used.
When a concave lens is used, it diverges the light before they get focused on the lens of the eye. This leads to focusing light on the retina itself and not in front of it. These lenses can be used either as eyeglasses or contact lenses.
Hence, a concave lens is used to correct myopia.

Additional Information:
Hypermetropia is a disorder in which the light focuses at the back of the retina instead of focusing on the retina. To correct this convex lens is used. Convex lenses are converging so these lenses cause light to focus on the retina.
Presbyopia is a disorder seen when the person starts ageing. To cure this, a bifocal lens is used which is a combination of concave and convex lens.

Note:
To answer such a question, you should know the difference between myopia, hypermetropia and presbyopia. A convex lens converges light so if a convex lens is used instead of a concave lens, the light will focus much more before the retina. This will cause the person to not be able to see anything. The lens used to correct these disorders should be of appropriate focal length.