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Other Eyes Defects

The maximum f...

Question

The maximum focal length of the eye-lens of a person is greater than its distance from the retina. The eye is :

A

always strained in looking at an object

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B

strained for object at large distance only

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C

strained for object at short distance only

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D

unstrained for all distances

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Solution

The correct option is C always strained in looking at an object
The eye is always strained in looking at an object because as the maximum focal length is greater than its distance from the retina the eye must be always strained to decrease the radius of curvature so as to decrease focal length.

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Similar questions

Q. The maximum focal length of the eye-lens of a person is greater than its distance from the retina. The eye is
(a) always strained in looking at an object
(b) strained for objects at large distances only
(c) strained for objects at short distances only
(d) unstrained for all distances

Q. The ciliary muscles of eye control the curvature of the lens in the eye and hence and alter the effective focal length of the system. When the muscles are fully relaxed, the focal length is maximum. When the muscles are strained, the curvature of lens increases. That means, radius of curvature decreases and focal length decreases. For a clear vision, the image must be on the retina. The image distance is therefore fixed for clear vision and it equals the distance of retina from eye lens. It is about

25 c m

for a grown up person.
A person can theoretically have clear vision of an object situated at any large distance from the eye. The smallest distance at which a person can clearly see is related to minimum possible focal length. The ciliary muscles are most strained in this position. For an average grown up person, minimum distance of the object should be around

25 c m

.
A person suffering from eye defects uses spectacles (eye glass). The function of lens of spectacles is to form the image of the objects within the range in which the person can see clearly. The image of the spectacle lens becomes object for the eye lens and whose image is formed on the retina.
The number of spectacle lens used for the remedy of eye defect is decided by the power of the lens required and the number of spectacle lens is equal to the numerical value of the power of lens with sign. For example, if power of the lens required is

+ 3 D

(converging lens of focal length

100 / 3 c m

), then number of lens will be

+ 3

.
For all the calculations required, you can used the lens formula and lensmaker's formula. Assume that the eye lens is equiconvex lens. Neglect the distance between the eye lens and the spectacle lens.
A near sighted man can clearly see objects only upto a distance of

100 c m

and not beyond this. The number of the spectacle lenses necessary for the remedy of this defect will be

Q. The ciliary muscles of eye control the curvature of the lens in the eye and hence and alter the effective focal length of the system. When the muscles are fully relaxed, the focal length is maximum. When the muscles are strained, the curvature of lens increases. That means, radius of curvature decreases and focal length decreases. For a clear vision, the image must be on the retina. The image distance is therefore fixed for clear vision and it equals the distance of retina from eye lens. It is about

2.5 c m

for a grown up person.
A person can theoretically have clear vision of an object situated at any large distance from the eye. The smallest distance at which a person can clearly see is related to minimum possible focal length. The ciliary muscles are most strained in this position. For an average grown up person, minimum distance of the object should be around

25 c m

.
A person suffering from eye defects uses spectacles (eye glass). The function of lens of spectacles is to form the image of the objects within the range in which the person can see clearly. The image of the spectacle lens becomes object for the eye lens and whose image is formed on the retina.
The number of spectacle lens used for the remedy of eye defect is decided by the power of the lens required and the number of spectacle lens is equal to the numerical value of the power of lens with sign. For example, if power of the lens required is

+ 3 D

(converging lens of focal length

100 / 3 c m

), then number of lens will be

+ 3

.
For all the calculations required, you can used the lens formula and lensmaker's formula. Assume that the eye lens is equiconvex lens. Neglect the distance between the eye lens and the spectacle lens.
A person can see objects clearly from distance

10 c m

\infty

. Then, we can say that the person is:

Q. Distance of eye lens from retina is

2 cm

for a person. Maximum focal length of the eye lens for the person is

1.96 cm

. Find the far point of the person

Q. A person is able to clearly see an object placed at

60 cm

from his eye. The focal length of the eye lens in this scenario is

2 cm

. What is the distance of the eye-lens from the retina?

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