Advantage and disadvantage of using an optical and electron microscope.

ADVANTAGE AND DISADVANTAGE OF USING AN OPTICAL AND ELECTRON MICROSCOPE

In this essay I will be talking about all the different types of Optical and Electron Microscopes and what there uses are and what the Advantage and Disadvantage of them both are.

Electron Microscope

An electron microscope uses electrons to illuminate an object. Because electrons have a smaller wavelength than light has it can resolve much smaller structures than light can. The resolution is very good. The minimum wavelength of an optical microscope is 500nm whereas the smallest wavelength of electrons in an electron microscope is round about 0.005nm.

The microscope has many different features. It has an electron gun so that it can emit electrons onto the specimen so it can create a magnified image. Magnetic lenses that create the magnetic fields are used to direct and focus the electrons onto the specimen. The microscope uses a vacuum system because electrons are easily scattered by air molecules so the microscope has a high vacuum. The can also produce images that the electrons have made.

There are two types of electron microscopes. The Transmission Electron microscope (TEM) and the Scanning Electron Microscope (SEM). In the TEM the electrons are directed onto the object, but some of the electrons are absorbed by the object so they do not reach the screen setting a dark image (electron dense). The specimen has to be cut very thin, so usually it is no more than 500nm thick. A fluorescent screen is placed under it so it can sample the magnified image. It can be capable of magnifying an object up to 1 million times.

The second type (SEM) creates ...

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The second type (SEM) creates a magnified image of the surface of the abject. In a SEM, a tightly focused electron beam moves over the sample. As it scans over the object, an image of the object is displayed on the monitor. The SEM has a magnifying power of over 100,000. SEM’s produce a detailed image of the surface of an abject providing a realistic three dimensional image.

Optical Microscope

The optical Microscope is the most used microscope. It uses light to create its magnified images. Some Optical Microscopes can magnify specimens by up to 2,000 times.

The compound Microscope consists of two lens systems, the OBJECTIVE and the OCULAR, put at opposite ends of closed tube. The objective consists of several lens elements that make up an enlarged image of the examined object. The lenses are set up so that the image formed by the objective lies at focal point of the ocular. The total magnification of the microscope is determined by the focal lengths of the two lens systems.

The specimens that are used for microscopic examination are transparent and are viewed by using light that passes through it. The specimen is usually under a glass slide. The stage of the microscope has a hole to let the light through to the specimen. under the stage there is either a mirror or an electrical light source that is directed to the specimen.

There have been many microscopes that have been constructed. One is the ultraviolet microscope. This microscope used the ultraviolet region of the spectrum to gain resolution to show detail.

The stereoscopic microscope, which is actually two low-powered microscopes arranged so that they converge on the specimen. These provide a three-dimensional image.

The Phase Contrast Microscope illuminates the specimen using a hollow cone of light. The cone of the light is narrow and it enters the field of view of the objective. This microscope is used for studying living tissue and used mostly for biology and medicine.