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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?
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
the biological/technical terms for the lens of eye losing flexibility resulting in a kind of long-sightedness in middle aged people.
A student is unable to see clearly the words written on the black board placed at a distance of approximately 3 m from him. Name the defect of vision the boy is suffering from. State the possible causes of this defect and explain the method of correcting it.
Name the defect of vision in a person:
whose near point is more than 25 on away.
Name the defect of vision in a person:
whose far point is less than infinity
What is the other name for
myopia
Name the defect of vision which makes the eye-lens cloudy resulting in blurred vision.
Name any two defects of vision which can be corrected by using spectacles.
Your friend can read a book perfectly well but cannot read the writing on blackboard unless she sits on the front row in class.
What type of lenses-converging or diverging-would an optician prescribe for her?
What are the two most common defects of vision (or defects of eye)? How are they corrected?
Name the defect of vision which can be corrected by a converging lens. Show clearly by a ray diagram how the lens corrects the defect.
Name the defect of vision which can be corrected by a diverging lens. Show clearly by a ray diagram how the lens corrects the defect.
The near-point of a person suffering from hypermetropia is at 50 cm from his eye. What is the nature and power of the lens needed to correct this defect? (Assume that the near-point of the normal eye is 25 cm).
A young man has to hold a book at arm's length to be able to read it clearly. The defect of vision is:
(a) astigmatism
(b) myopia
(c) presbyopia
(d) hypermetropia
Name the following:
The photosensitive pigment present in the rods of the retina.
Name the following:
The eye defect caused due to shortening of the eye ball from front to back.
Explain the terms ‘adaptation’ and ‘accommodation’ with reference to the eye.
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.
Have a look at the posture of this girl who is reading a book and answer the questions which follow:
Name the problem she is facing.
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.
Given below is a diagram depicting a defect of the human eye? Study the same and answer the question that follow:
Name the parts labeled 1 to 4.
Anuja cannot see the blackboard writing but she can see nearby things.
(a) What is the eye defect she is suffering from?
(b) State the possible reason for her defect.
(c) How is it corrected
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?
In what two whys is a yellow spot different from the blind spot?
Give Reason:
Older people require glasses to read and write.
Explain the Term: Hypermetropia
Explain the Term: Astigmatism
Name the following:
The defect of the human eye caused due to the uneven surface of the cornea.
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:
Choose the Odd One Out:
Due to elongation of _______ and increase in curvature of the eye lens, a person cannot see distant objects clearly.
What are the causes of ‘Myopia’?
A person cannot see distinctly objects kept beyond 2 m. This defect can be corrected by using a lens of power:
Assertion: Myopia is the defect of vision in which a person cannot see distant objects clearly.
Reason: This due to eye-ball being too short.
A teacher drew the diagram of the heart on the blackboard and told the students to copy it in their notebooks. Mahesh couldn't see the diagram clearly as it appeared blurred to him.
- Name the defect of the eye Mahesh is suffering from.
- Where is the image formed in this defect?
- Mahesh consults an eye doctor and is prescribed suitable lenses to correct the defect. Which type of lens do his spectacles have?
