Advertisements
Advertisements
प्रश्न
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?
उत्तर
The person is suffering from an eye defect called myopia. In this defect, the image is formed in front of the retina. Hence, a concave lens is used to correct this defect of vision.
Object distance, u = infinity = ∞
Image distance, v = – 80 cm
Focal length = f
According to the lens formula,
`1/"v" - 1/"u" = 1/"f"`
`1/(-80) - 1/(-∞) = 1/"f"`
`1/(-80) = 1/"f"`
f = −80 cm = −0.80 m ...(concave lens)
∴ power of modified lens,
P = `1/"f"`
= `1/(-0.80 "m")`
= −1.25 D
A concave lens of power −1.25 D is required by the person to correct his defect.
संबंधित प्रश्न
List three common refractive defects of vision. Suggest the way of correcting these defects.
The kind of lens required to correct Myopia
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 an old man
A person is unable to see distinctly the objects closer than 1 m. Name the defect of vision he is suffering from. Draw ray diagrams to illustrate the cause of the defect and its correction by suitable lens.
A person cannot read newspaper placed nearer than 50 cm from his eyes. Name the defect of vision he is suffering from. Draw a ray diagram to illustrate this defect. List its two possible causes. Draw a ray diagram to show how this defect may be corrected using a lens of appropriate focal length.
What eye defect is hypermetropia? Describe with a ray diagram how this defect of vision can be corrected by using an appropriate lens.
State the main functions of the following:
Tears
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.
Name the following:
The photosensitive pigment present in the rod cells of the retina.
Choose the correct answer :
Presbyopia is a disease of _____________
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.
Solve the following question:
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?
Draw a neat labeled diagram to show how hypermetropia can be rectified.
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
Myopia and hypermetropia can be corrected by:
Myopia may arise due to ____________.
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?
