Ray Optics and Optical Instruments

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The near point is the minimum distance from the eye at which an object can be seen clearly without strain. For a normal young eye, it is about 7-8 cm, but increases with age to 100-200 cm or more in e

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The least distance of distinct vision is the distance up to which the human eye can see objects clearly without any strain. For a normal human eye, this distance is taken as D = 25 cm. This is used as

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Angular magnification (magnifying power) = ratio of angle subtended by image at eye to angle subtended by object at unaided eye when both are at least distance of distinct vision. Linear magnification

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For a simple microscope: M = β/α where β is angle subtended by image, α is angle subtended by object. Since angles are small: M = tan β/tan α = (A'B'/D)/(AB/D) = A'B'/AB. Using similar triangles and l

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Given: f = 5 cm, D = 25 cm Using formula: M = 1 + D/f M = 1 + 25/5 = 1 + 5 = 6 Therefore, the magnifying power is 6 times.

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Normal adjustment is when the final image is formed at infinity. This causes least strain on the eye as the eye muscles are relaxed when viewing objects at infinity. For simple microscope in normal ad

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A compound microscope has two convex lenses: (1) Objective - short focal length, small aperture, faces object (2) Eye-piece - short focal length, large aperture, faces eye. Object placed just beyond f

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M = β/α = (A''B''/AB) = (A''B''/A'B') × (A'B'/AB) = me × mo where me = magnification by eye-piece = 1 + D/fe mo = magnification by objective = vo/uo Therefore: M = (vo/uo)(1 + D/fe) For practical purp