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Question 26: NCERT Solutions for 12th Class Physics: Chapter 9-Ray Optics and Optical Instruments
A myopic person has been using spectacles of power – 1.0 dioptre for distant vision. During old age, he also needs to use separate reading glass of power + 2.0 dioptres. Explain what may have happened.
Solution:
Myopic person uses spectacles of power – 1.0 dioptre or concave lens of focal length ƒ =
= -100 cm in order to observe clearly object at infinity. Far point of the person can be calculated as
Similarly if the person uses spectacles of power + 2.0 dioptre then he must be using convex lens of power + 2.0 dioptre. Focal length and near point can be calculated as
Thus the person also has the defect of hypermetropia and has a near point 50 cm. So having both defects he needs different lenses for distant vision and to see closer objects.
Check the complete chapter with solutions.
NCERT Solutions for 12th Class Physics: Chapter 9-Ray Optics and Optical Instruments