explain the following terms used in relation to defects in vision and correction provided by them :
1 myopia
2 biofocal lenses
3 far -sightendness
why is the normal eye unable to focus on an object placed within 10 cm from the eye
Answers
myopia - in this defect we can't see far object clearly we use concave lens for correction
bifocal lenses are used by those can't see near by object nor far object
far sightedness is a defect in which people can't see near by object we use convex lens for correction
A normal eye can't focuses on 10 vm object because near point of a normal eye is 25cm
i hope my answer will help u
Answer:
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(a) (i) Myopia: Short-sightedness is caused due to excessive curvature in cornea or elongation of eyeball. Image is formed before of the retina. So, a concave lens is used to correct it.
(ii) Astigmatism: The inability to focus the light in both vertical and horizontal lines is called astigmatism. It is caused due to varying curvature in lens both horizontally and vertically. It is . corrected by using cylindrical lens.
(iii) Bifocal lenses: These are used to correct presbyopic eye. These contain lenses with upper concave and lower convex surface. Presbyopia arises with age.
(iv) Far-sightedness: Hypermetropia or far-sightedness is caused due to greater focal length of eye lens and/or when eyeball becomes smaller. Image is formed beyond the retina and can be corrected using a convex lens.
(b) The focal length of the lens cannot be changed up to an extent that objects nearer than 25 cm can be viewed (its near point is 25 cm). So it is not able to focus for 10 cm.