A person suffering from presbyopia needs bifocal lens. If he needs two lens of power −4·0 dioptre and + 2·0 dioptre, which one of these two lenses is for the correction of distant vision and what is its focal length ?

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TextPower of a LensPresbyopiaCorrection of Vision Defects Using LensesCBSE PYQ

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An old person is suffering from an eye defect caused by weakening of ciliary muscles and diminishing flexibility of the eye lens. If the defect of vision is 'a' which can be corrected by lens 'b', then 'a' and 'b' respectively are :

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The power of a lens 'X' is – 2·5 D. Name the lens and determine its focal length in cm. For which eye defect of vision will an optician prescribe this type of lens as a corrective lens ?

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The numerical values of the focal lengths of two lenses A and B are 10 cm and 20 cm respectively. Which one of the two will show higher degree of convergence/divergence ? Give reason to justify your answer.

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Draw a ray diagram to show the refraction of a ray of light through a rectangular glass slab when it falls obliquely from air into glass.

TextRefraction Through Rectangular Glass SlabImage Formation by Convex LensImage Formation by Concave LensSign Convention for Spherical LensesMagnification by Spherical LensesPower of a LensMyopia or Near-sightednessCorrection of Vision Defects Using Lenses

State Snell's law of refraction of light.

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