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प्रश्न
Observe the figure and answer the following questions:
- Name the defect of vision represented in the above figure.
- State the reasons for this defect.
- How is it corrected?
- Draw the diagram to show the correction of this defect.
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उत्तर
- In the figure, Myopia or Nearsightedness defect of vision is represented.
- There are two reasons for this defect.
1. The curvature of the cornea and the eye lens increases. The muscles near the lens can not relax so the converging power of the lens remains large.
2. The eyeball elongates so that the distance between the lens and the retina increases. - This defect can be corrected by using spectacles with concave lenses of proper focal length. This lens diverges the incident rays and these diverged rays can be converged by the lens in the eye to form the image on the retina. The focal length of the concave lens is negative, so a lens with negative power is required for correcting nearsightedness. The power of the lens is different for different eyes depending on the magnitude of their nearsightedness.
Correction of Nearsightedness
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संबंधित प्रश्न
What is myopia?
List three common refractive defects of vision. Suggest the way of correcting these defects.
A student suffering from myopia is not able to see distinctly the objects placed beyond 5 m. List two possible reasons due to which this defect of vision may have arisen. With the help of ray diagrams, explain
(i) why the student is unable to see distinctly the objects placed beyond 5 m from his eyes.
(ii) the type of the corrective lens used to restore proper vision and how this defect is corrected by the use of this lens.
(b) If, in this case, the numerical value of the focal length of the corrective lens is 5 m, find the power of the lens as per the new Cartesian sign convention
Name the defect of vision in a person:
whose near point is more than 25 on away.
Which defect of vision can be rectified:
by using a convex lens?
What is the other name for
hypermetropia
Name the defect of vision in which the eye-lens loses its power of accommodation due to old age.
What is the other name of old age hypermetropia?
Name the body part with which the terms myopia and hypermetropia are connected.
A student sitting in the last row of the class-room is not able to read clearly the writing on the blackboard.
How can this defect by corrected?
An eye has a near point distance of 0.75 m. What sort of lens in spectacles would be needed to reduce the near point distance to 0.25 m? Also calculate the power of lens required. Is this eye long-sighted or short-sighted?
Though a woman can see the distant object clearly, she cannot see the nearby objects clearly. She is suffering from the defect of vision called:
(a) long-sight
(b) short-sight
(c) hind-sight
(d) mid-sight
The picture given here shows a person wearing 'half-moon' spectacles. What sort of eye-defect do do you think he has? Why are these particular spectacles useful to him?
A person can read a book clearly only if he holds it at an arm's length from him. Name the defect of vision:
if the person is an old man
Which part of the eye is grafted in a needy patient from a donated eye?
Name the following:
The eye defect caused due to shortening of the eye ball from front to back.
You do not enjoy watching a movie from a very short distance from the screen in a cinema hall. Why?
Given below is a diagram depicting a defect of the human eye. Study the same and answer the question that follow:
Name the defect shown in the diagram.
State one role of ciliary muscles in the human eye.
What eye defect is hypermetropia? Describe with a ray diagram how this defect of vision can be corrected by using an appropriate lens.
Name the following:
The photosensitive pigment present in the rod cells of the retina.
Select the odd one in the following series:
Endolymph, Tympanic membrane, Semi-circular canal, Blind spot.
Write whether the following is true or false:
A convex lens is used for correcting myopia.
Given alongside is a diagram depicting a defect of the human eye. Study the same and then answer the questions that follow:
(i) Identify the defect.
(ii) Name the parts labelled 1, 2 and 3.
(iii) Give labelled two possible reasons for this eye defect.
(iv) Draw a labelled diagram to show how the above mentioned defect is rectified.
The near point of the eye of a person is 50 cm. Find the nature and power of the corrective lens required by the person to enable him to see clearly the objects placed at 25 cm from the eye?
What type of lens is used to correct Astigmatism?
Given below is a diagrammatic representation of a defect of the human eye:
(i) Identify the defect.
(ii) Mention two reasons for the above defect.
(iii) State how the defect can be rectified.
(iv) Name the part of the eye responsible for maintaining the shape of the eyeball.
Choose the Odd One Out:
Nearsightedness: elongated eyeball : : farsightedness: _______
Write scientific reason.
Nearsightedness, this defect can be corrected by using spectacles with concave lens.
Myopia and hypermetropia can be corrected by:
Which of the following statement is correct?
Myopia may arise due to ____________.
Draw ray diagram showing myopic eye.
State reasons for Myopia. With the help of ray diagrams, show the:
- image formation by a myopic eye, and
- correction of myopia using an appropriate lens.
Name the following:
Two kinds of accomodations.
