Advertisements
Advertisements
प्रश्न
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?
Advertisements
उत्तर
A person suffering from myopia can correct the defect by wearing spectacles with concave lenses. In order to find the power of the concave lens required, we have to first calculate its focal length.
Given that the far point of the myopic person is 2 m from the eye (the person can see an object kept at infinity if the image of the object is formed at the far point of 2 m from the eye).
u = ∞ (distance of the object)
v = -2 m (far point in front of the lens)
f = ? (focal length)
The focal length can be calculated using the lens formula `1/v-1/u=1/f`
Substituting the values in the formula, we get `1/-2-1/oo=1/f`
∴ f = -2 m
Now that we know the focal length of the concave lens, the power can be calculated.
Power P=`1/f("inmeters")`
p=`1/-2=-0.5` diptres
Therefore, the power of the concave lens required to rectify the defect is -0.5 dioptres.
APPEARS IN
संबंधित प्रश्न
A student is unable to see clearly the words written on the blackboard placed at a distance of approximately 4 m from him. Name the defect of vision the boy is suffering from. Explain the method of correcting this defect.
Draw ray diagram for the:-
(i) defect of vision and also
(ii) for its correction.
Explain two possible reasons of myopia. How can it be corrected? Explain with a suitable diagram.
The kind of lens required to correct Myopia
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 far point is less than infinity
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.
Though a woman can see the distant object clearly, she cannot see the nearby objects clearly. She is suffering from the defect of vision called:
(a) long-sight
(b) short-sight
(c) hind-sight
(d) mid-sight
The defect of vision in which the eye-lens of a person gets progressively cloudy resulting in blurred vision is called:
(a) myopia
(b) presbyopia
(c) colourblindness
(d) cataract
A short-sighted person has a near point of 15 cm and a far point of 40 cm.
(a) Can he see clearly an object at a distance of:
(i) 5 cm?
(ii) 25 cm?
(iii) 50 cm?
(b) To see clearly an object at infinity, what kind of spectacle lenses does he need?
The near point of a long-sighted person is 50 cm from the eye.
(a) Can she see clearly an object at:
(i) a distance of 20 cm?
(ii) at infinity?
Enumerate the common defects of vision, their causes and the possible methods of correcting them.
Name the common defects of the eye.
Name an old age eye defect. Why is it caused?
Give Reason:
Deficiency of vitamin A causes night blindness.
Differentiate between:
Short-sightedness and Long-sightedness.
What type of lens is used to correct Astigmatism?
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.
Which of the following statement is correct?
Complete the following table by observing the given figures:
| Figure → |  |
 |
| Points ↓ | ||
| (a) Name of the defect | ______ | ______ |
| (b) Position of the image | ______ | ______ |
| (c) Lens used to correct the defect | ______ | ______ |
