Questions
Q1. What is meant by power of accommodation of the eye?
Answer:
The power of accommodation of the eye is the ability of the eye lens to adjust its focal length by changing its curvature. This allows the eye to focus clearly on objects at varying distances, from nearby to far away, by the contraction or relaxation of the ciliary muscles.
Q2. A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore proper vision?
Answer:
A person with myopia (near-sightedness) has a far point closer than infinity, meaning distant objects are focused in front of the retina. To correct this, a concave lens of suitable power is used. Concave lenses diverge light rays before they enter the eye, allowing the image to form on the retina. The required focal length of the lens should be equal to the far point distance (1.2 m) so that objects at infinity appear to be at this distance.
Q3. What is the far point and near point of the human eye with normal vision?
Answer:
For a human eye with normal vision, the far point is at infinity, meaning it can see distant objects clearly without any strain. The near point is the minimum distance at which objects can be seen clearly and distinctly without strain, which is about 25 cm for a young adult.
Q4. A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?
Answer:
The student likely suffers from myopia (near-sightedness). In this defect, the eye can see nearby objects clearly, but distant objects (like the blackboard) appear blurred because the image is formed in front of the retina. This can be corrected by using a concave lens of appropriate power, which diverges the incoming light rays slightly so that they focus correctly on the retina.