Electron Microscopes

Biology - Electron Microscopes Electron Microscopy is the use of Electron Microscopes. Electron Microscopes have a very high resolving power and a high magnification, and thus are used to view small objects with greater magnification and detail than a light microscope. There are two different types of electron microscopes, each with different abilities and limitations. This essay will analyse and discuss the functions and limitations of each different type individually, and then conclude with comparisons. Transmission Electron Microscope This type of electron microscope allows the user to view a 2d image of a cross section of a sample. It has a maximum resolution of 1 nm and a maximum magnification of 250,000 x. The good resolution is due to the short wavelengths of electrons, which is 0.005 nm. In a TEM the electrons are fired from an electron gun, which is part of the cathode, and are drawn through the microscope by the anode. The electrons pass through the specimen, which must be very thin, and prepared in a certain way for exactly that reason. The specimen preparation process will be explained in detail later in the essay. There are three electromagnetic lenses in a TEM. Electromagnetic lenses are used because firstly electron beams cannot pass through glass, and secondly, as electrons are charged particles, they are affected by a magnetic field. The first is called

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Norman Lockyer observatory trip

Norman Lockyer observatory trip For our visit we went to the Norman Lockyer observatory to find out more about the nights skies. The two ways they studied the skies were telescopes and spectroscopes. The Norman locker observatory or NLO is based in Sidmouth. Here is a picture of the observatory Norman Lockyer, (1836-1920) founded the NLO in 1912 There are two types of telescopes, Reflecting and Refracting. The NLO has 4 refracting telescopes, and 2 reflecting telescopes. Refracting telescopes This explains how a refracting telescope works. Good and bad factors about refractors Achromatic refractors use lenses that are not extensively corrected to prevent chromatic aberration, which is a rainbow halo that sometimes appears around images seen through a refractor. Instead, they usually have "coated" lenses to reduce this problem. Apochromatic refractors use either multiple-lens designs or lenses made of other types of glass (such as fluorite) to prevent chromatic aberration. Apochromatic refractors are much more expensive than achromatic refractors. Refractors have good resolution, high enough to see details in planets and binary stars. However, it is difficult to make large objective lenses (greater than 4 inches or 10 centimetres) for refractors. Refractors are relatively expensive, if you consider the cost per unit of aperture. Because the aperture is limited, a

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The Principles and Limitations of Electron Microscopy.

The Principles and Limitations of Electron Microscopy. An Electron Microscope is a type of microscope that makes use of a beam of electrons rather than visible light. Which is due to the fact that the wavelength of electrons is much smaller than the wavelength of visible light, an Electron Microscope not only gives a high magnification but it also has high resolution. This means that details can be seen clearly. An Electron Microscope is very similar to a Light Microscope in the ways in which it works but, instead of using glass lenses to focus a beam of light, it uses magnets to focus a beam of electrons. Electrons are very small, so they are scattered if they hit molecules in the air due to this they must travel through a vacuum. Specimens that are to be examined must be cut into very thin sections, and these must be treated so that they can be examined in these conditions. The variety of chemical processes that are carried out in this preparation may change the appearance considerably. Features which have been introduced in this way are known as artefacts and care needs to be taken in interpreting electron micrographs because of the possible presence of artefacts. An examination of a specimen using an Electron Microscope can yield the following information: Topography: The surface features of an object or "how it looks", it's texture; direct relation between these

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The Use and Operation of the Light and Electron Microscope

The Use and Operation of the Light and Electron Microscope Light microscopes were first used in the seventeenth century, famously by the scientist Robert Hooke; the man that first named 'cells'. It was not until the nineteenth century however that microscopy became popular. Before this time, the lenses had not been of high enough quality to view images clearly, in the early nineteenth century improvements were made and the identification of cell structures began. Problems with resolution then became apparent; a wave length shorter than light needed to be used in order to improve the clarity of image produced; Electron microscopes were developed as a solution; both Ultraviolet light and X-rays have shorter wave lengths but it was found that these were extremely difficult to focus. Electrons, however, are negatively charged particles; this gives the advantage of being able to focus them easily, by use of electromagnets. These electromagnets act in exactly the same way as a lens would on a Light Microscope. How light microscopes work In a compound light microscope; a light source is located underneath the stage. The light goes through a condenser lens and through the specimen, the resulting light is then passed through two more lenses, both used to magnify the image and focus towards the ocular. The lenses used indicate the resulting magnification of the specimen. Lenses are

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Explain how the electron microscope has affected our knowledge of cell form and structure

Wednesday 9th October 2002. Explain how the electron microscope has affected our knowledge of cell form and structure. Electron microscopes use a beam of electrons instead of light to produce images of specimens. There are two types of electron microscope: - Transmission electron microscope Scanning electron microscope How an electron microscope works. Electrons are generated in an electron gun, which applies a high voltage of about 100,000 volts through a filament called a tungsten filament. The filament is heated to above 3000 degrees Kelvin, which is roughly 3273 degrees Celsius. Applying an increasing negative voltage to a cathode assembly, which is located just above an anode plate, accelerates the electrons. The anode plate has a tiny hole in its centre, the electron beam is sent through this hole creating a very concentrated beam of electrons. This beam is focused using magnetic coils that act like the condenser lenses that you find on a light microscope. The specimen is on a plate just above a second magnetic coil, which acts as an objective lens. The objective lens resolves the structure and magnifies it slightly. Focusing the specimen can be achieved by altering the electric current through the lens. More magnetic coils act as projector lenses, which enlarge the image. All specimens in electron microscopy are placed in a vacuum, this means that all

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Research into Telescopes

Telescopes The first record of a device that acted like a telescope was made in October 1608. It came from Holland where the state discussed the patent applications of Hans Lipperhey and Jacob Metius. The records describe a device for "seeing faraway things as though nearby." It was the most simple form of telescope consisting of a tube and a concave lens at one end and a convex lens at the other and gave a magnifying power of three or four times. The earliest known illlustration of a telescope. Giovanpattista della Porta included this sketch in a letter written in August 1609 But the man who made telescopes really famous was Galileo Galilei. By October/November 1609 he had constructed a 24x telescope and made observations of the moon and discovered the four major moons of Jupiter. Galileo's telescopes were simple refracting telescopes that were of less quality than those you can buy cheaply in the high street. They were based on simple convex lens to focus the light and magnify that image. Convex lens's work on the principle of refraction. When a wave enters a material that is denser than the original substance, it 'bends' towards the normal (the normal being perpendicular to the plane the denser material). The opposite occurs when the wave leaves the denser material. Upon leaving the denser material the wave is 'bent' away from the normal. This is called

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Bradford Museum of Film and Photography

Bradford Museum of Film and Photography Our physics group went on a trip to the Bradford Museum of Film and Photography to find out more about physics. We went to find out about new ideas of physics and also to reinforce ideas we had already covered in class. The areas of physics we were going to focus on was the use of light and lenses and the way they are used in everyday products. At the museum we visited an area called The Magic Factory, which was all to do with the ideas and applications of physics. At the museum an exhibit, which interested me, was the pinhole camera exhibit. This is because it gave a very clear image of the clock tower in the distance through a tiny little pinhole using a converging lens. There was a few different options you could choose to test how a pinhole camera works, there was the option to use a bigger hole which gave a very blurred image of the clock tower and there was also an option to use three pinholes at the same time which gave an image which showed the clock tower overlapping each other three times. The small pinhole however was the most successful to view a sharp image on the screen the image is upside down due to the converging lens. In a pinhole camera the smaller the hole is the sharper image however this has limitations as the sharper the image the less light there will be and the image wont be as bright. A pinhole camera

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Comparing the Light and Electron Microscope

Comparing the Light and Electron Microscope In this essay I am going to be comparing the light and electron microscope, I will look at the advantages and disadvantages of each microscope and then analyse my findings to see if one is better than the other. The light, or optical microscope as it is also known was invented in the 17th century, it has been refined in many ways over the years but it is essentially still the same. The light microscope works by; light rays from a light source beneath the stage are through to glass lenses in series. The two lenses are called the objective lens and the ocular (eyepiece) lens. Depending on their strength these two lenses on their own routinely provide magnifications of up to 400 times. There is a limit to the amount of detail the light microscope can show, this limit is set by the resolving power. The resolving power is the minimum distance by which two points must be separated in order for them to be perceived as two separate points, rather than a single fused image. For the light microscope this distance is approximately 0.2µm. So in theory it might seem possible to magnify an object indefinitely by means of glass lenses in series. This has been put into practice and has only produced a larger and fuzzier picture; so the resolution is not improved and no more detail is visible. The resolution of the light microscope is imposed by

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Measurement of the focal lengths of a concave lens and a convex mirror

Kwun Tong Government Secondary School Advanced Level Physics (TAS) Experiment Report Experiment No.: 3 Title: Measurement of the focal lengths of a concave lens and a convex mirror Date of Experiment: 2006/11/28 Mark: Sch. Code 2114 TAS Group 5 Name: Chan Man Lok Class: S.6C Class No.: 6 Objective: . To measure the focal length of a concave lens with the help of an auxiliary convex lens and the lens formula 2. To measure the focal length of a convex mirror with the help of an auxiliary convex lens Apparatus: Instrument Convex lens x 1 Concave lens x 1 Convex mirror x 1 Metre rule x 1 White screen x 1 Ray box with a fine gauze grid x 1 Lens holder x 2 Theory: Measurement of the focal length of a concave lens using an auxiliary convex lens: . Position the screen to catch the real image formed by the auxiliary convex lens 2. Add the concave lens between the convex lens and the screen and reposition the screen to catch the image of fine grid again 3. Calculate the focal length of the concave lens f by using the lens formula: By using real-is-positive convention, u will be taken as negative. Measurement of the focal length of a convex mirrorusing an auxiliary convex lens . Position the screen to catch the real image formed by the auxiliary convex lens 2. Add the convex mirror between the screen

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Describe the principles and limitations of transmission and scanning electron microscopes. Specific reference should be made to magnification and resolution

Describe the principles and limitations of transmission and scanning electron microscopes.Specific reference should be made to magnification and resolution Introduction Microscopy has a major role in cytology.From the very beginning researchers have tried to develop ways of looking directly at living cells.This examination has revealed much about the morphology of cells and tissues.In recent years,development in microscopes,dyes,staining and preparatory techniques have helped reveal even more about the structure and function of cells.Microscopes have a certain magnification and resolving power.In any microscope the the resolving power is more important than the magnification.The resolving power of a microscope is the least distance between two objects where the microscope can still distinguish the objects as being separate.It is a measure of detail that can be seen.A microscope with a high resolving power enables us to view images with a high resolution.With a low resolution they would be viewed as one object.Microscopes with a high magnification are only able to increase the size of the object that is being viewed.The resolution will be the same.(ie the object will still lack clarity and appear fuzzy).The two types of microscopes are electron and light microscopes. Principles and Limitations of light microscopy Light microscopes function by focussing a beam of light on

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