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प्रश्न
Explain with the help of labelled ray diagram, the defect of vision called myopia and how it is corrected by a lens.
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उत्तर
Myopia is a defect of vision because of which a person is unable to see distant objects clearly but has normal near vision. Myopia occurs because the converging power of the eye lens is greater than normal and the images of distant objects are formed in front of the retina. As a result, a person with myopia cannot see these objects clearly. In certain other cases, myopia occurs because the eyeball is too long and the distance of the retina from the eye lens is large. This, too, causes the formation of images in front of the retina. The far point of a myopic eye is closer than infinity. The following ray diagram explains the myopic eye and how the defect can be corrected by using concave lenses. A concave lens diverges the light rays from distant objects to form virtual images of the objects at the far point of eye. The eye lens then easily focusses the light rays from the far point to form clear images on the retina.
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संबंधित प्रश्न
Write the importance of ciliary muscles in the human eye. Name the defect of vision that arises due to gradual weakening of the ciliary muscles. What types of lenses are required by the person suffering from this defect to see the objects clearly?
Akshay, sitting in the last row in his class, could not see clearly the words write on the blackboard. When the teacher noticed it, he announced if any student sitting in the front row could volunteer to exchange his seat with Akshay. Salman immediately agreed to exchange his seat with Akshay. He could now see the words written on the blackboard clearly. The teacher thought it fit to send the message to Akshay’s parents advising them to get his eyesight checked.
In the context of the above event, answer the following questions:-
(a) Which defect of vision is Akshay suffering from? Which type of lens is used to correct this defect?
(b) State the values displayed by the teacher and Salman.
(c) In your opinion, in what way can Akshay express his gratitude towards the teacher and Salman?
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?
Name the defect of vision in a person:
whose near point is more than 25 on away.
Name the defect of vision which makes the eye-lens cloudy resulting in blurred vision.
Explain with the help of labelled ray-diagram, the defect of vision called hypermetropia, and hot it is corrected by a lens.
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).
Which part of the eye is grafted in a needy patient from a donated eye?
What is meant by optical illusion? Give one example.
What eye defect is hypermetropia? Describe with a ray diagram how this defect of vision can be corrected by using an appropriate lens.
Give Reason:
Why do we see clearly in the central region of the retina?
Give Reason:
Deficiency of vitamin A causes night blindness.
Differentiate between:
Myopia and Hypermetropia.
Draw a neat labeled diagram to show how hypermetropia can be rectified.
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.
Study the following diagram carefully and then answer the questions that follow. The diagram is depicting a defect of the human eye :
(i) Identify the defect shown in the diagram.
(ii) Give two possible reasons for the above defect.
A person cannot see distinctly objects kept beyond 2 m. This defect can be corrected by using a lens of power:
A person needs a lens of power –4.5 D for correction of her vision.
- What kind of defect in vision is she suffering from?
- What is the focal length of the corrective lens?
- What is the nature of the corrective lens?
When do we consider a person to be myopic or hypermetropic? Explain using diagrams how the defects associated with myopic and hypermetropic eye can be corrected?
Correlate the given sequence:
Hypermetropia : Convex lens : ______ : Concave lens
