Difference Between Light Microscope and Electron Microscope

The word 'microscope' is a conflation of two Greek words: 'mikros' (small) and 'skopein' (to look). As becomes evident by the name, a microscope is a device with the help of which we can see enlarged images of objects that are too small for us to see with our naked eyes. The science that deals with investigating small particles are called microscopy, and the microscope is very obviously the most prominent tool of that science. Similarly, objects that are too small to be observed without a microscope are called microscopic.

A microscope can function in different ways. The most common type of microscope is the optical microscope, also called the light microscope, because it works by reflecting the visible light on the sample that is to be observed. Optical microscopes can commonly be found in educational institutions' physics or biology labs like schools and universities. They are very useful in demonstrating the working, function and application of a microscope.

But microscopes can also function by making the sample hit by a beam of electrons. Light is an electromagnetic wave, and the wavelength of the wave decides the resolution of the microscope. So, for example, if blue light is used to observe the sample in a microscope, then that microscope will have a higher resolution than the microscope using a light of a bigger wavelength like a red light. An electron microscope uses high-speed electrons to observe the sample. These high energy electrons have much smaller wavelengths than the visible light wave. Therefore an electron microscope can achieve great magnification.

Other than optical and electron, microscopes also work by detecting the photon emission by a sample or by scanning a sample using a probe from a short distance across the sample.

Optical Microscope

Optical microscopes, also called light microscopes, are the oldest microscopes that were invented. Optical microscopes work by using visible light and a system of lenses to produce an imaginary and enlarged image of any sample put under the microscope's lens. The present compound microscope design that uses two lenses was developed in the seventeenth century. An optical microscope in its simplest design can be just a single lens that magnifies the image. The optical microscope works by forming an imaginary image of the sample that appears to be farther than the actual distance of the sample from the lens. This allows for easy observation of the sample without putting strain on the eyes. Since its first invention, several improvements in the design have been made to improve upon the microscope's resolution.

The optical microscope usually has one eyepiece, but microscopes with two eyepieces have been invented. In that case, both the eyepieces give the same image. However, in a stereo microscope, both the eyepieces deliver slightly different images to produce a 3-D effect, much like the 3-D glasses used in the movie theatres to convert a 2-D image to a 3-D one. In the case of a stereo microscope, a camera is used to capture the image to be converted to 3-D. This camera is called a micrograph.

Any sample in the microscope can be lighted in many different ways: for transparent samples, the light may be introduced from behind the sample. But for the sample to be visible, the sample has to be tinted by a colouring agent. For opaque, solid objects, the light may be introduced from the microscope itself, called the bright field, or it may be lit from sideways by an external source, called a a dark field.

Electron Microscope

Electron microscope works on accelerated beams of electrons. When these beams strike the sample, they produce magnetic fields, and these magnetic fields are used by an optical system that is analogous to the optical lenses of a light microscope to produce a picture of the sample or the part of a sample under observation. As a result, the electron microscope has a much higher resolution than the light microscope. Since it works on beams of electrons, which can have wavelengths up to 100,000 times shorter than the wavelengths of photons, the electron microscope can give up to 10,000,000 times better resolving power than a light microscope.

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