Question

2. Essay: Roughly how big is the smallest object that can be seen with a conventional light microscope? Why? Give an example of a technique that can be used to see smaller objects, and explain how it works.

Answer 1

Conventional light microscope uses visible light and a system of of lenses to generate magnified image of object. The object is placed at a stage and it is seen through the eye piece of microscope. Now, depending upon the lense used , we get magnified image of object. More bigger image will form if the object size is comparable to wavelength of light used.Usually, the maximum magnification power of it is limited to around 1000x because of limited resolving power of visible light. So, visible light cannot be used to magnify the object which is smaller than its wavelength. With the help of it, one can seean object as long as milimeters and as small as 0.2 micrometer.

Object smaller than this can be seen using scanning electron microscope. It uses electron beam to get diffracted from the object and make its magnified image. Its wavelength is shorter and hence can be used to see object as small as atom (10-10m ). The electron beam is first accelerated through 100kev voltage and transmits to the specimen. The electron beam will get scattered and now carries the information of structure of specimen which is magnified by the lenses.

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