Question

(a) Name two defects of vision. Mention two main causes of each

defect.

(b) A person uses spectacles having lenses of focal length – 2.0 m.

Determine the nature and power of the lenses used in his

spectacles.


class 10th science
​

Answer 1

Answer:

Explanation:

A. The ability to see is called vision. Sometimes the eye of a person cannot focus on the image of an object on the retina properly, resulting in defects of vision and they are:

Myopia (short-sightedness or near-sightedness)

Myopia is caused because of:

Due to high converging power of eye lens

Due to eyeball being too long

Myopia is corrected by using spectacles containing concave lenses.  Hypermetropia (Long-sightedness or far-sightedness

Hypermetropia is caused because of:  

Due to low converging power of eye lens

Due to eyeball being too short

Hypermetropia is corrected by using spectacles containing convex lenses.

B. f=  

p

1  =  

−2

100

​ cm

 =−50 cm

The defect of eye will be nearsighted.