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Home » a) What is long-sightedness? State the two causes of long-sightedness. With the help of ray diagram, show:i) the eye defect long sightednessii) correction of long-sightedness using a lensb) An eye has a near point distance of 0.72m. What sort of lens in spectacles would be needed to reduce the near point distance to 0.25m? Also, calculate the power of lens required. Is this eye long-sighted or short-sighted?c) An eye has far point of 2m. What type of lens in spectacles would be needed to increase the far point to infinity? Also, calculate the power of lens required. Is this eye long-sighted or short-sighted?
a) What is long-sightedness? State the two causes of long-sightedness. With the help of ray diagram, show:
i) the eye defect long sightedness
ii) correction of long-sightedness using a lens
b) An eye has a near point distance of 0.72m. What sort of lens in spectacles would be needed to reduce the near point distance to 0.25m? Also, calculate the power of lens required. Is this eye long-sighted or short-sighted?
c) An eye has far point of 2m. What type of lens in spectacles would be needed to increase the far point to infinity? Also, calculate the power of lens required. Is this eye long-sighted or short-sighted?
CBSE | Class 10 | Lakhmir Singh | Physics | The Human Eyes And The Colourful World
a) What is long-sightedness? State the two causes of long-sightedness. With the help of ray diagram, show:
i) the eye defect long sightedness
ii) correction of long-sightedness using a lens
b) An eye has a near point distance of 0.72m. What sort of lens in spectacles would be needed to reduce the near point distance to 0.25m? Also, calculate the power of lens required. Is this eye long-sighted or short-sighted?
c) An eye has far point of 2m. What type of lens in spectacles would be needed to increase the far point to infinity? Also, calculate the power of lens required. Is this eye long-sighted or short-sighted?

a) Long sightedness is a vision problem in which a person can’t see items that are far away yet can see objects that are close by. The two main reasons of long-sightedness are as follows:

I The eye lens’ focal length is too lengthy.

ii) The eyeball has shrunk in size.

Long-sightedness ray diagram:

Ray diagram of correction of long sightedness:

b) To correct long sightedness, a convex lens is utilised.

Given,

u = -0.25m is the object distance.

v = -0.75m image distance

1/v-1/u=1/f

f = 3/8m f = 3/8m f = 3/8m

2.67D = P = 1/f

The eye has a lengthy sightedness to it.

c) You’ll need a concave lens.

Given,

u = infinite, object distance

v = 2m image distance

f = -2m

1/f = -0.5D P = 1/f = -0.5D

eed a concave lens.

i

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