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?
Advertisements
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
A student suffering from myopia is not able to see distinctly the objects placed beyond 5 m. List two possible reasons due to which this defect of vision may have arisen. With the help of ray diagrams, explain
(i) why the student is unable to see distinctly the objects placed beyond 5 m from his eyes.
(ii) the type of the corrective lens used to restore proper vision and how this defect is corrected by the use of this lens.
(b) If, in this case, the numerical value of the focal length of the corrective lens is 5 m, find the power of the lens as per the new Cartesian sign convention
What is the other name of old age hypermetropia?
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.
Name the defect of vision which can be corrected by a diverging lens. Show clearly by a ray diagram how the lens corrects the defect.
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?
Name an old age eye defect. What happens in it?
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.
An old man cannot see objects closer than 1 m from the eye clearly. Name the defect of vision he is suffering from. How can it be corrected? Draw ray diagram for the (i) defect of vision and also (ii) for its correction.
What is Hypermetropia (far sightedness)?
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.
Give Reason:
Why do we see clearly in the central region of the retina?
What type of lens is used to correct Hypermetropia?
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.
Write scientific reason.
Nearsightedness, this defect can be corrected by using spectacles with concave lens.
Observe the given below the figure, correct it and explain and write about the concept depicted in this figure.
Differentiate the eye defects: Myopia and Hypermetropia
Which of the following statement is correct?
Draw ray diagram showing myopic eye.
Observe the figure whether it is correct or not and explain the phenomenon.
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.
