Advertisements
Advertisements
Question
An old man cannot see objects closer than 1 m from the eye clearly. Name the defect of vision he is suffering from. How can it be corrected? Draw ray diagram for the (i) defect of vision and also (ii) for its correction.
Advertisements
Solution
The person is suffering from presbyopia. It is a common defect of vision, which generally occurs at old age. A person suffering from this type of defect of vision cannot see nearby objects clearly and distinctively. A presbyopic eye has its near point greater than 25 cm and it gradually increases as the eye becomes older. Presbyopia is caused by the
1. weakening of the ciliary muscles
2. reduction in the flexibility of the eye lens
This defect can be corrected by using a convex lens of appropriate power.
(i) Ray diagram showing presbyopia
(ii) Ray diagram showing correction of presbyopia
APPEARS IN
RELATED QUESTIONS
What is the other name for
myopia
What is the scientific name of
short-sightedness
Name the defect of vision which can be corrected by a diverging lens. Show clearly by a ray diagram how the lens corrects the defect.
An eye has a far point of 2 m. What type of lens in spectacles would be needed to increase the far point to infinity? Also calculate the power of lens required. Is this eye long-sighted or short-sighted?
To read a book held at a distance of 25 cm, will she need converging or diverging spectacle lenses?
Name the following:
The photosensitive pigment present in the rods of the retina.
When do we consider a student sitting in the class to be myopic? List two causes of this defect. Explain using a ray diagram how this defect of eye can be corrected.
Write scientific reason.
Nearsightedness, this defect can be corrected by using spectacles with concave lens.
Complete the following table by observing the given figures:
| Figure → |  |
 |
| Points ↓ | ||
| (a) Name of the defect | ______ | ______ |
| (b) Position of the image | ______ | ______ |
| (c) Lens used to correct the defect | ______ | ______ |
