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प्रश्न
Explain two possible reasons of myopia. How can it be corrected? Explain with a suitable diagram.
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उत्तर
Possible reasons of myopia:-
(i) Ciliary muscles do not relax sufficiently. Therefore, the converging power of the eye lens becomes high.
(ii) The distance between the eye lens and the retina increases (relative to the normal eye) as the eyeball is lengthened (elongated) or the eye lens is curved.
Correcting myopia:-
(i) Myopia is corrected using a suitable concave lens. Light rays are diverged by the concave lens before they strike the eye lens.
(ii) A concave lens of appropriate power is chosen to produce the required divergence. Hence, after the converging action of the eye lens, the image is formed on the retina.
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संबंधित प्रश्न
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.
About 45 lac people in the developing countries are suffering from corneal blindness. About 30 lac children below the age of 12 years suffering from this defect can be cured by replacing the defective cornea with the cornea of a donated eye. How and why can students of your age involve themselves to create awareness about this fact among people?
Which defect of vision can be rectified:
by using a convex lens?
What is the other name for
myopia
Name one defect of vision (or eye) which cannot be corrected by any type of spectacle lenses.
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?
A student sitting in the last row of the class-room is not able to read clearly the writing on the blackboard.
Name the type of defect he is suffering from.
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?
What are the two most common defects of vision (or defects of eye)? How are they corrected?
Explain with the help of labelled ray diagram, the defect of vision called myopia and how it is corrected by a lens.
A person suffering from the eye-defect myopia (short-sightedness) can see clearly only up to a distance of 2 metres. What is the nature and power of lens required to rectify this defect?
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?
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 a young man
Name the following:
The eye defect caused due to shortening of the eye ball from front to back.
Differentiate between members of the following pair with reference to what is asked in the bracket.
Rods and cones (sensitivity).
Name an old age eye defect. What happens in it?
What is meant by optical illusion? Give one example.
You do not enjoy watching a movie from a very short distance from the screen in a cinema hall. Why?
What eye defect is hypermetropia? Describe with a ray diagram how this defect of vision can be corrected by using an appropriate lens.
When do we consider a student sitting in the class to be myopic? List two causes of this defect. Explain using a ray diagram how this defect of eye can be corrected.
Given below is a diagram depicting a defect of the human eye? Study the same and answer the question that follow:
Give two possible reasons for this defect of the eye in human beings.
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?
Give Reason:
Deficiency of vitamin A causes night blindness.
Differentiate between:
Short-sightedness and Long-sightedness.
Explain the Term: Astigmatism
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.
With respect to human eye explain:
(i) How is the image formed on the retina?
(ii) How is the amount of light entering the eye-controlled?
(iii) What type of lens is used for the correction of ‘Long sight’ defect?
(iv) With the help of a ray, diagram show the defect of the eye and then its correction after the use of a lens.
Mention, if the following statement is True or False
Hypermetropia is a defect of the eye caused due to the eyeball elongation
Choose the Odd One Out:
Nearsightedness: elongated eyeball : : farsightedness: _______
Write scientific reason.
Nearsightedness, this defect can be corrected by using spectacles with concave lens.
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.
Myopia may arise due to ____________.
Draw ray diagram showing myopic eye.
Observe the figure whether it is correct or not and explain the phenomenon.
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.
A person is unable to see clearly a poster fixed on a distant wall. He however sees it clearly when standing at a distance of about 2 m from the wall.
- Draw ray diagram to show the formation of image by his eye lens when he is far away from the wall.
- List two possible reasons of this defect of vision.
- Draw ray diagram to show the correction of this defect using appropriate lens.
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?
