16.8 Optical Instruments and Magnifying Power

The limitations of the human eye in observing very small and very distant objects can be overcome to a certain extent with the help of mirrors and lenses. Such artifacts are called optical instruments. Here we shall consider three such instruments : magnifying glass or simple microscope, compound microscope and astronomical telescope (refracting type).

The optical instruments essentially magnify the apparent size of the object. The apparent size of the object i.e. the size of the image of the object as seen by the eye, decreases with distance of the - same object - object from the eye; correspondingly, the angle subtended by the object or the eye also decreases. The angle subjected by an object at the eye (angle a) is taken as the measure of the apparent size of the object. ( see figure 20 )

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Index

Light

16.1 Laws of Reflection at plane surfaces
16.2 Mirrors
16.3 Laws of Refraction at plane surfaces, Refractive Index and Critical Angle
16.4 Refraction at curved spherical surfaces and Lens maker’s formula
16.5 Lenses
16.6 Refraction in Prisms, Prism Formula
16.7 Dispersion of Light, Angular Dispersion and Dispersive Power
16.8 Optical Instruments and Magnifying Power

Chapter 17