Does Short-sightedness (Myopia) Or Long-sightedness (Hypermetropia) Imply Necessarily that the Eye Has Partially Lost Its Ability of Accommodation? If Not, What Might Cause These Defects of Vision? - Physics


Does short-sightedness (myopia) or long-sightedness (hypermetropia) imply necessarily that the eye has partially lost its ability of accommodation? If not, what might cause these defects of vision?



A myopic or hypermetropic person can also possess the normal ability of accommodation of the eye-lens. Myopia occurs when the eye-balls get elongated from front to back. Hypermetropia occurs when the eye-balls get shortened. When the eye-lens loses its ability of accommodation, the defect is called presbyopia.

Concept: Optical Instruments: the Eye
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Chapter 9: Ray Optics and Optical Instruments - Exercise [Page 348]


NCERT Physics Class 12
Chapter 9 Ray Optics and Optical Instruments
Exercise | Q 25 | Page 348


A virtual image, we always say, cannot be caught on a screen. Yet when we ‘see’ a virtual image, we are obviously bringing it on to the ‘screen’ (i.e., the retina) of our eye. Is there a contradiction?

A person looking at a person wearing a shirt with a pattern comprising vertical and horizontal lines is able to see the vertical lines more distinctly than the horizontal ones. What is this defect due to? How is such a defect of vision corrected?

What should be the distance between the object and the magnifying glass if the virtual image of each square in the figure is to have an area of 6.25 mm2. Would you be able to see the squares distinctly with your eyes very close to the magnifier?

The angle subtended at the eye by an object is equal to the angle subtended at the eye by the virtual image produced by a magnifying glass. In what sense then does a magnifying glass provide angular magnification?

What is the height of the final image of the tower if it is formed at 25 cm?

The muscles of a normal eye are least strained when the eye is focussed on an object

When objects at different distances are seen by the eye, which of the following remain constant?

The focal length of a normal eye-lens is about

The distance of the eye-lens from the retina is x. For a normal eye, the maximum focal length of the eye-lens

A man wearing glasses of focal length +1 m cannot clearly see beyond 1 m

When we see an object, the image formed on the retina is
(a) real
(b) virtual
(c) erect
(d) inverted

Mark the correct options.
(a) If the far point goes ahead, the power of the divergent lens should be reduced.
(b) If the near point goes ahead, the power of the convergent lens should be reduced.
(c) If the far point is 1 m away from the eye, divergent lens should be used.
(d) If the near point is 1 m away from the eye, divergent lens should be used.

A person looks at different trees in an open space with the following details. Arrange the trees in decreasing order of their apparent sizes.

Tree Height(m) Distance from the eye(m)
A 2.0 50
B 2.5 80
C 1.8 70
D 2.8 100


Can virtual image be formed on the retina in a seeing process?

A normal eye has retina 2 cm behind the eye-lens. What is the power of the eye-lens when the eye is (a) fully relaxed, (b) most strained?

A nearsighted person cannot see beyond 25 cm. Assuming that the separation of the glass from the eye is 1 cm, find the power of lens needed to see distant objects.

A myopic adult has a far point at 0.1 m. His power of accomodation is 4 diopters.

  1. What power lenses are required to see distant objects?
  2. What is his near point without glasses?
  3. What is his near point with glasses? (Take the image distance from the lens of the eye to the retina to be 2 cm.)


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