Question

What type of lens is used to correct (a) hypermetropia (b) myopia?

Answer 1

Hint : A person suffering from hypermetropia has the condition that the incoming light into his/her eyes is being focused behind the retina. We use the proper lens to correctly focus the incoming light. For a person suffering from myopia, the light is focused in front of his/her retina. A suitable lens can fix this problem.

Complete step by step answer
(a) A person suffering from hypermetropia can see the objects at a distance clearly but has problems with the objects closer to them. The closer objects appear to blur. It is the condition that the incoming light into his/her eyes is being focused behind the retina. This natural focussing of light is done by the lens in human eyes. If they get damaged or weak, their focal length may change. This will lead to incoming light focussing behind the retina.
We can use a convex lens of suitable focal length such that it helps to focus the incoming light properly on the retina. A convex lens helps to bring the focus of the combined lens system near. Thus, focus the light on the retina.
The focal length of the convex lens will depend from person to person. Someone suffering from severe hypermetropia will need a different lens as compared to someone suffering from slightly.
(b)A person suffering from myopia can see the objects closer to them clearly but has problems with the objects away from them. The distant objects appear to blur. It is the condition that the incoming light into his/her eyes is being focused in front of the retina. This may happen due to old age or a damaged lens.
We can use a concave lens of suitable focal length to help the lens in our eyes to focus the incoming light into the retina. A concave lens helps to push the focus of the combined lens system away. Thus, focus the light on the retina.
The focal length of the used concave lens depends on the severity of myopia the person is suffering from.

Note
To solve such a problem, you need a clear understanding of how a convex or concave lens changes the focal length of a combined lens system. With given distances, we can also calculate the shift in the focus of a lens system after introducing a concave or convex lens.