Question 14 Marks
The lens of the eye does little of the bending of the light rays. Most of the refraction is done at the front surface of the cornea which also acts as a protective covering. The lens acts as a fine adjustment for focussing at different distances. This is accomplished by the ciliary muscle, which change the curvature of the lens so that its focal length is changed. To focus on a distant object, the muscles are relaxed and the lens is thin and parallel rays focus at the focal point (on the retina). To focus on a nearby object, the muscles contract, causing the centre of the lens to be thicker, thus shortening the focal length so that images of nearby objects can be focused on the retina, behind the focal point. This focusing adjustment is called accommodation.
The closest distance at which the eye can focus clearly is called the near point of the eye. A given person's far point is the farthest distance at which an object can be seen clearly. To check your own near point, place this book close to your eye and slowly move it away until the type is sharp.
A large part of the population have eyes that do not accommodate within the normal range of $25 cm$ to infinity, or have some other defect. Two common defects are near-sightedness and far-sightedness. Both can be corrected to a large extent with lenses-either eyeglasses or contact lenses.
(i) The ciliary muscle muscles of a normal eye are in their (i). most relaxed (ii). most contracted state. In which of the two cases is the focal length of the eye-lens more?
(ii) What is the least distinct of vision of young man?
(iii) What is persistence of vision?
or
(iv) What is meant by power of accommodation of the eye?
The closest distance at which the eye can focus clearly is called the near point of the eye. A given person's far point is the farthest distance at which an object can be seen clearly. To check your own near point, place this book close to your eye and slowly move it away until the type is sharp.
A large part of the population have eyes that do not accommodate within the normal range of $25 cm$ to infinity, or have some other defect. Two common defects are near-sightedness and far-sightedness. Both can be corrected to a large extent with lenses-either eyeglasses or contact lenses.
(i) The ciliary muscle muscles of a normal eye are in their (i). most relaxed (ii). most contracted state. In which of the two cases is the focal length of the eye-lens more?
(ii) What is the least distinct of vision of young man?
(iii) What is persistence of vision?
or
(iv) What is meant by power of accommodation of the eye?
Answer
View full question & answer→(i) In most relaxed state
(iii) $25 cm$
(ii) The impression or sensation of the image remains on the retina for about $1 / 16^{\text {th }}$ of a second. It is called persistence of vision.
or
(iv) Power of accommodation is the ability of the eye lens to focus near and far objects clearly on the retina by adjusting its focal length.
(iii) $25 cm$
(ii) The impression or sensation of the image remains on the retina for about $1 / 16^{\text {th }}$ of a second. It is called persistence of vision.
or
(iv) Power of accommodation is the ability of the eye lens to focus near and far objects clearly on the retina by adjusting its focal length.
