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प्रश्न
Write scientific reason.
Nearsightedness, this defect can be corrected by using spectacles with concave lens.
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उत्तर
- Nearsightedness arises due to slight elongation of the eyeball causing an increase in the distance between the eye lens and the retina or due to an increase in the curvature of the cornea and eye lens resulting in increased converging power.
- As a result, light from a distant object arriving at the eye-lens gets converged at a point in front of the retina.
- When a concave lens of suitable focal length is placed between the eye and object, due to the diverging effect of the concave lens, the image gets focussed on the retina.
Thus, nearsightedness can be corrected by using spectacles with a concave lens.
संबंधित प्रश्न
What is myopia?
Millions of people in the developing countries of the world are suffering from corneal blindness. These persons can be cured by replacing the defective cornea with the cornea of a donated eye. A charitable society of your city has organised a campaign in your neighbourhood in order to create awareness about this fact. If you are asked to participate in this mission, how would you contribute in this noble cause?
(i) State the objective of organising such campaigns.
(ii) List two arguments which you would give to motivate the people to donate their eyes after death.
(iii) List two values which are developed in the persons who actively participate and contribute in such programmes.
A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore proper vision?
Explain two possible reasons of myopia. How can it be corrected? Explain with a suitable diagram.
What is the far point of a person suffering from myopia (or short-sightedness)?
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?
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 person having short-sight cannot see objects clearly beyond a distance of 1.5 m. What would be the nature and power of the corrective lens to restore proper vision?
A person cannot see the distant objects clearly (though he can see the nearby objects clearly). He is suffering from the defect of vision called:
(a) cataract
(b) hypermetropia
(c) myopia
(d) presbyopia
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
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 a young man
Differentiate between members of the following pair with reference to what is asked in bracket.
Myopia and hyperopia (cause of the defect)
Name an old age eye defect. What happens in it?
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.
A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?
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.
Have a look at the posture of this woman who is reading a book and answer the questions which follow:
What kind of looking glasses she needs?
Differentiate between:
Short-sightedness and Long-sightedness.
Explain the Term: Hypermetropia
Explain the Term: Presbyopia
Explain the Term: Astigmatism
Give Technical Term:
The path which responsible for protecting the eye from sweat.
What type of lens is used to correct Hypermetropia?
Complete the following sentence with appropriate word :
An inability to focus on nearby objects due to loss of elasticity of the lens with age is called Iris.
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.
Due to elongation of _______ and increase in curvature of the eye lens, a person cannot see distant objects clearly.
Nearsightedness: elongated eyeball : : farsightedness: _______
Nearsightedness : concave lens : : farsightedness : _______
Given below is a diagram showing a defect of vision. Name the defect of vision and draw an accurately labelled diagram to correct this defect.
Differentiate the eye defects: Myopia and Hypermetropia
Which of the following statement is correct?
Correlate the given sequence:
Hypermetropia : Convex lens : ______ : Concave lens
Observe the figure whether it is correct or not and explain the phenomenon.
Observe the following diagram and answer questions following it:
- Identify the defect of vision shown.
- List its two causes.
- Name the type of lens used for the correction of this defect.
