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Least Distance of distinct vision (D) :

The closest distance that the 'normal' human eye can observe clearly; without any strain to the eye is called the least distance of distinct vision.

In connection with optical instruments the object would be considered to be held whenever feasible at the least distance of distinct vision for determining its apparent size even if the actual position of the object may not be at (D). Usually D = 25 cm.

Magnifying Power (M) of an Optical Instrument :

It is defined as the ratio of the apparent size of the final image i.e. angle subtended by the image at the position of eye (b) to the apparent size of the object i.e. angle subtended by the object at the eye (a).

Simple Microscope (Magnifying glass) and its Magnifying Power (M) :

The property of a convex lens to produce a virtual, erect and magnified image on the same side of the lens as the object allows the convex lens to be used as an optical instrument called simple microscope.



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 makerís 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

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