HEY guys plz explain me this question...
3. Answer question numbers 3.1–3.4 on the basis of your
understanding of the following paragraph and the
related studied concepts.
The ciliary muscles of eye control the curvature of
the lens in the eye and hence can alter the effective
focal length of the system. When the muscles are
fully relaxed, the focal length is maximum. When the
muscles are strained the curvature of lens increases
(that means radius of curvature decreases) and focal
length decreases. For a clear vision the image must
be on retina. The image distance is therefore fixed for
clear vision and it equals the distance of retina from
eye-lens. It is about 2.5 cm for a grown-up person.
A person can theoretically have clear vision of
objects situated at any large distance from the eye.
The smallest distance at which a person can clearly
see is related to minimum possible focal length, The
ciliary muscles are most strained in this position. For
an average grown-up person minimum distance of
object should be around 25 cm.
A person suffering for eye defects uses spectacles
(Eye glass). The function of lens of spectacles is
to form the image of the objects within the range
in which person can see clearly. The image of the
spectacle-lens becomes object for eye-lens and whose
image is formed on retina.
The number of spectacle-lens used for the remedy
of eye defect is decided by the power of the lens
required and the number of spectacle-lens is equal to
the numerical value of the power of lens with sign. For
example power of lens required is +3D (converging
lens of focal length 100/3 cm) then number of lens
will be +3.
For all the calculations required you can use the
lens formula and lens maker’s formula. Assume that
the eye lens is equiconvex lens. Neglect the distance
between eye lens and the spectacle lens.
3.1 What do you mean by the ciliary muscles? [1]
Ans : The muscles which are used to the change in
the focal length of eye lens by changing radii of
curvature is known ciliary muscles.
<------ This one I know..
3.2 What is the minimum focal length of eye lens of a
normal person? [1]
Ans : 25/11 cm. <------ How ??
3.3 What is the maximum focal length of eye lens of
normal person? [1]
Ans : 2.5 cm. <--------- How??
3.4 A near-sighted man can clearly see object only up-
to a distance of 100 cm and not beyond this. What
is the number of the spectacles lens necessary for
the remedy of this defect? [1]
plz solve this part for me.
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Answer:
3.4 the person can see object
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