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Question
In a Std. X class, out of 40 students, 10 students use spectacles, 2 students have positive power and 8 students have negative power of lenses in their spectacles.
Answer the following questions :
(i) What does the negative power indicate?
(ii) What does the positive power indicate?
(iii) Generally which type of spectacles do most of the students use?
(iv) What defect of eyesight do most of the students suffer from?
(v) Give two possible reasons for the above defect.
Answer the following questions :
(i) What does the negative power indicate?
(ii) What does the positive power indicate?
(iii) Generally which type of spectacles do most of the students use?
(iv) What defect of eyesight do most of the students suffer from?
(v) Give two possible reasons for the above defect.
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Solution
(i) The negative power indicates that the students are suffering from 'Myopia' or 'Short sightedness'.
(ii) The positive power means that the students are suffering form 'Hypermetropia' or 'Long sightedness'.
(iii) Among all the 40 students 10 are using spectacles and among them 8 are having negative power, that means most of the students uses corrective lenses have a negative optical power (i.e., have a net concave effect).
(iv) Most of the students were suffering from 'Myopia'.
(v) The two possible reasons for myopia are :
(a) Elongation of the length of the eyeball, or
(b) Shortening of the focal length of the eye lens.
(ii) The positive power means that the students are suffering form 'Hypermetropia' or 'Long sightedness'.
(iii) Among all the 40 students 10 are using spectacles and among them 8 are having negative power, that means most of the students uses corrective lenses have a negative optical power (i.e., have a net concave effect).
(iv) Most of the students were suffering from 'Myopia'.
(v) The two possible reasons for myopia are :
(a) Elongation of the length of the eyeball, or
(b) Shortening of the focal length of the eye lens.
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