Question

Explain with a neat digram , the working of a compound microscope and astronomical telescope . obtain expression for its magnifying power .

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Answer 1

Explanation:

Ray diagram of a compound microscope. Compound microscope: It is an optical device used to see a highly magnified image of tiny objects.

Construction: It consists of two convex lenses of short focal length arranged co-axial at the free end of the tube, at a suitable fixed distance. Objective: It is a convex lens of very short focal length f0 and small aperture, kept near the object. Working Principle: The most commonly used microscope for general purposes is the standard compound microscope. It magnifies the size of the object by a complex system of the lens arrangement. It has a series of two lenses;

(i) the objective lens close to the object to be observed and

(ii) the ocular lens or eyepiece, through which the image is viewed by eye. Light from a light source (mirror or electric lamp) passes through a thin transparent object The objective lens produces a magnified ‘real image’ first image) of the object. This image is again magnified by the ocular lens (eyepiece) to obtain a magnified ‘virtual image’ (final image), which can be seen by eye through the eyepiece. As light passes directly from the source to the eye through the two lenses, the field of vision is brightly illuminated. That is why; it is a bright-field microscope. Magnifying power: The ratio of the angle subtended by the eye by the final virtual image, to the angle subtended at the eye by the object When the final image is formed at the least distance of distinct vision, magnifying power is, For the image to be formed at infinity, ue = fe and By making focal length of the objective lens small