Advertisements
Advertisements
प्रश्न
Write scientific reason.
Nearsightedness, this defect can be corrected by using spectacles with concave lens.
Advertisements
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
In a Std. X class out of 40 students 10 students use spectacles, 2 students have positive power and 8 students have negative power of lenses in their spectacles.
Answer the following questions:
(1) What does the negative power indicate?
(2) What does the positive power indicate?
(3) Generally which type of spectacles do most of the students use?
(4) What defect of eyesight do most of the students suffer from?
(5) Give two possible reasons for the above defect.
Do you know that the corneal-impairment can be cured by replacing the defective cornea with the cornea of the donated eye? How and why should we organise groups to motivate the community members to donate their eyes after death?
List three common refractive defects of vision. Suggest the way of correcting these defects.
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?
The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?
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.
What is the other name for
hypermetropia
What is the scientific name of
short-sightedness
Name one defect of vision (or eye) which cannot be corrected by any type of spectacle lenses.
Your friend can read a book perfectly well but cannot read the writing on blackboard unless she sits on the front row in class.
- Is she short-sighted or long-sighted?
- 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.
- How can this defect by corrected?
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?
Differentiate between myopia and hypermetropia.
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?
What is long-sightedness? State the two causes of long-sightedness (or hypermetropia). With the help of ray diagrams, show:
(i) the eye-defect long-sightedness.
(ii) correction of long-sightedness by using a lens.
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
By closing the eyes and gently pressing them by your palms, you may see some specks of brilliant light. How do you get this sensation while there is no light entering your eyes?
What eye defect is hypermetropia? Describe with a ray diagram how this defect of vision can be corrected by using an appropriate lens.
What is Hypermetropia (far sightedness)?
Draw a ray diagram to show how Hypermetropia is defect can be corrected using a lens.
Distinguish between the following pair of words:
Myopia and hypermetropia
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?
Name an old age eye defect. Why is it caused?
Differentiate between:
Short-sightedness and Long-sightedness.
Give Technical Term:
The path which responsible for protecting the eye from sweat.
What type of lens is used to correct Hypermetropia?
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:
Observe the given below the figure, correct it and explain and write about the concept depicted in this figure.
A person cannot see distinctly objects kept beyond 2 m. This defect can be corrected by using a lens of power:
Assertion: Concave mirrors are used as reflectors in torches, vehicle head lights and in search lights.
Reason: When an object is placed beyond the center of curvature of a concave mirror, the image formed is real and inverted.
Draw ray diagram showing myopic eye.
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?
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.
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.
- What are the two conditions shown in sections A and B of the eye as applicable to her.
- What kind of reading glasses does she need?
 |
 |
| A | B |
