Advertisements
Advertisements
Question
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?
Advertisements
Solution
a) (i) A short-sighted person with a near point of 15 cm and a far point of 40 cm in front of the eye cannot clearly see an object at a distance of 5 cm because he can see an object only when it is placed at his near point (i.e., 15 cm).
(b) A short-sighted person can clearly see an object at a distance of 25 cm as it the normal near point of the eye. Moreover, the person's far point is located at 40 cm from the eye.
(c) The person cannot see the object clearly as it is at a distance of 50 cm, which is beyond his far point.
(d) In order to see an object clearly at infinity, the person should use concave lenses in his spectacles. A concave lens first diverges the light rays from the object at infinity to form a virtual image at the eye's far point. The eye lens then easily focusses the rays from the eye's far point to form a clear image on the retina.
APPEARS IN
RELATED QUESTIONS
A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore proper vision?
Explain two possible reasons of myopia. How can it be corrected? Explain with a suitable diagram.
What is the other name for
myopia
What is the scientific name of
long-sightedness?
Name the defect of vision in which the eye-lens loses its power of accommodation due to old age.
Name the defect of vision which can be corrected by a diverging lens. Show clearly by a ray diagram how the lens corrects the defect.
Explain with the help of labelled ray-diagram, the defect of vision called hypermetropia, and hot it is corrected by a lens.
What is short-sightedness? State the two causes of short-sightedness (or myopia). With the help of ray diagrams, show:
(i) the eye-defect short-sightedness.
(ii) correction of short-sightedness by using a lens.
What is meant by optical illusion? Give one example.
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.
What is Hypermetropia (far sightedness)?
A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?
Have a look at the posture of this woman who is reading a book and answer the questions which follow:
What kind of looking glasses she needs?
What type of lens is used to correct Astigmatism?
Choose the Odd One Out:
Write scientific reason.
Nearsightedness, this defect can be corrected by using spectacles with concave lens.
Assertion: Concave mirrors are used as reflectors in torches, vehicle head lights and in search lights.
Reason: When an object is placed beyond the center of curvature of a concave mirror, the image formed is real and inverted.
Draw ray diagram showing myopic eye.
Observe the following diagram and answer questions following it:
- Identify the defect of vision shown.
- List its two causes.
- Name the type of lens used for the correction of this defect.
