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
Given below is a diagram showing a defect of human eye. Study it and answer the following questions.
(i) Name the defect shown in the figure.
(ii) Give reason for this defect of eye in human being.
(iii) Name the type of lens used to correct the eye defect.
List three common refractive defects of vision. Suggest the way of correcting these defects.
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
A man can read the number of a distant but clearly but he finds difficulty in reading a book.
What type of spectacle lens should he use to correct the defect?
An eye has a near point distance of 0.75 m. What sort of lens in spectacles would be needed to reduce the near point distance to 0.25 m? Also calculate the power of lens required. Is this eye long-sighted or short-sighted?
To read a book held at a distance of 25 cm, will she need converging or diverging spectacle lenses?
Name the following:
The photosensitive pigment present in the rods of the retina.
Explain the terms ‘adaptation’ and ‘accommodation’ with reference to the eye.
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.
A student cannot see a chart hanging on a wall placed at a distance of 3 m from him. Name the defect of vision he is suffering from. How can it be corrected? Draw ray diagrams for the (i) defect of vision and also (ii) for its correction.
Given below is a diagram depicting a defect of the human eye? Study the same and answer the question that follow:
Draw a labeled diagram to show how the above mentioned defect is rectified using the lens named above.
Have a look at the posture of this woman who is reading a book and answer the questions which follow:
What are the two conditions shown in sections A and B of the eye as applicable to her?
Explain the Term: Hypermetropia
The diagram given below represents the cross-section of the human eye:
(i) Name the parts labeled 1—12.
(ii) What is the function of the part marked ‘10’?
(iii) What would happen if part ‘5’ is damaged or cut?
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:
Myopia and hypermetropia can be corrected by:
A student sitting at the back of the classroom cannot read clearly the letters written on the blackboard. What advice will a doctor give to her? Draw ray diagram for the correction of this defect.
Name the following:
Two kinds of accomodations.
