Short Answer TypeA student wants to project the image of a candle flame on the walls of school laboratory by using a lens:
(a) Which type of lens should be use and why?
(b) At what distance in terms of focal length 'F' of the lens should be place the candle flame so as to get (i) a magnified, and (ii) a diminished image respectively on the wall? Draw ray diagram to show the formation of the image in each case?
(a) List three common refractive defects of vision. Suggest the way of correcting these defects.
(b) About 45 lac people in the developing countries are suffering from corneal blindness. About 30 lac children below the age of 12 years suffering from this defect can be cured by replacing the defective cornea with the cornea of a donated eye. How and why can students of your age involve themselves to create awareness about this fact among people?
(a) The three common refractive defects of vision are as follows:
Myopia (short-sightedness): Concave lenses of appropriate power are used for the correction of this defect.
Hypermetropia (far-sightedness): It is corrected by using spectacles having convex lenses of appropriate power.
Presbyopia: This defect is corrected using bifocal lenses of appropriate power in which the upper part consists of a concave lens to correct myopia and the lower part consists of a convex lens to correct hypermetropia.
b) After death, a person can donate his/her eyes to the person having corneal blindness. It will help him/her see the beautiful world. One can register themselves to eye-donation camps where they will preserve our eyes after our death and donate it to the needy.
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