The Principles and Limitations of Scanning and Transmission Electron Microscopes
The Principles and Limitations of Scanning and Transmission Electron Microscopes Electron microscopes were first developed due to the limitations of light microscopes (3). The smallest object that can be viewed by any microscope is half the wavelength of light used, and objects smaller than this cannot be seen. This is because the object has to be large enough to interfere with the waves radiation. Light has a wavelength between 400-700nm, so the smallest object that can be viewed using visible light is 200nm(3). By the early 1930's all the possible scientific progress on understanding the inner parts of cells had been made, and scientists wanted to see more detail. Max Knoll and Ernst Ruska then developed the electron microscopes in 1931 (7). Electron microscopes use the same principles as light microscopes, but a beam of electrons is used instead of a beam of light. Electron beams have a wavelength of about 0.005nm. This short wavelength means much smaller objects can be seen (3). The resolution of a microscope is its ability to distinguish between two objects that are very close together. Magnification shows the objects as one larger image. The shorter the wavelength, the better the resolution. Therefore the resolution of an electron microscope is better than a light microscope. The magnification is also better. Magnifications of x250 000 can be obtained with an electron
What are Light Microscopes?
Pass1 What are Light Microscopes? What does the word microscope mean: The first part of the word "Micro" means tiny. The "scope" part means to look at or view. Microscopes are tools that are used too enlarge images of small objects so that they can be studied. A light microscope is an instrument made up of two lens they are eyepiece lens and the object lens combined they produce a much greater magnification that what is possible with just one single lens. The microscope also has a variety of knobs to focus the picture seen thought the microscope. The light microscope is also known as the compound microscope this is because it uses more than one lens. The light microscope uses visible light to detect small objects; the microscope consists of an optical instrument that magnifies the image of an object. It is probably the most used research tool in biology. The total magnification is calculated by multiplying the magnification of the two lenses inside the microscope. Images looked at under the light microscope are reversed and inverted. Functions Of The Components Seen Under A Light Microscope Cytoplasm: is a partly fluid material, which can flow slowly and in which many other substances are suspended such as large fat and protein molecules. Many of the chemical reactions take place in the cytoplasm, which will provide the cell with energy and allow it to build up
Telescopes - research into types and properties of telescopes
Telescopes are instruments that magnify distant objects. Astronomers use telescopes to study the planets, stars, and other floating bodies. In most telescopes a lens or mirror is used to form an image of an object. The image may be viewed through an eyepiece or recorded on photographic film or by electronic devices. Telescopes produce images of objects too far away to be seen by the unaided human eye. The Dutch optician Hans Lippershey designed the first telescope in 1608, when he mounted two glass lenses in a narrow tube. Within a year the Italian astronomer Galileo built a similar device and became the first person to use a telescope to study the sky. Optical Telescopes Optical Telescopes use a lens or mirror to collect and focus light waves. There are three main types of optical telescopes. Refracting telescope Refracting telescopes also known as refractors have a large lens called an objective lens at one end of a long, narrow tube. The lens is convex on both sides so that the middle of the lens is thicker than the edges. The glass slows the light rays as they pass through the lens. (A wave is slowed most in the middle of the lens where the glass is thickest). The lens therefore causes the entire crest of the wave to arrive at the focus at the same time. Refractors with a magnifying eyepiece invert the image so that it appears upside down as astronomical observations
ELECTRON MICROSCOPY This is the act of using electron microscopes. Electron Microscopes are scientific instruments that use a beam of highly energetic electrons to examine objects on a very fine scale. Electron microscopes can be used to view the topography (surface), the morphology (the shape and size of the particles making up the object) and also the composition (elements and compounds the object is composed of and how many: in case of cell organelles). Electron microscopes were introduced or developed due to the limitation of light microscopes. This is because the resolving power of a microscope depends on the wavelength of the electromagnetic radiation used; because the light microscope uses only the visible part (light) of the electromagnetic spectrum whose shortest wavelength is 400 nanometre (violet light), therefore objects smaller than half of the wavelength (200nm) cannot be viewed using a light microscope. E.g. cell organelle ribosome is 20nm and can never be seen using a light microscope. As electron microscopes uses electrons, which are negatively charged and beams of electrons have a very short wavelength. This type of microscope has a very high magnification and resolution power. They are two major types of electron microscopes the first type originally developed: The Transmission Electron Microscope, which is quite similar to the light electron microscope
When two objects are placed close enough to each other or are a great enough distance, there will come a point where your eyes will be unable to distinguish the two objects apart. Determine the resolving power of your eyes.
Liban Ahmed Experiment 4 September 20, 2003 Resolving Power Purpose When two objects are placed close enough to each other or are a great enough distance, there will come a point where your eyes will be unable to distinguish the two objects apart. Determine the resolving power of your eyes. Hypothesis If two strands of hair are placed a foot away in front of white background, then the resolving power of the eyes will be approximately half a millimeter or 0.5 mm. Materials * Glass slide and cover slip * Two human hairs * Dissecting needles * Microscope Procedure . Brought a microscope to the lab area making sure to use both hands to carry the microscope and that the cord was not dangling. 2. Looked through the instructions making sure there were no problems that could be posed. 3. Organized the lab area and prepared all equipment including slides and the microscope. 4. Placed two human hairs on the slide 1 mm apart and placed the cover slip above. 5. Placed the slide in front of a white background and examined from a distance of one foot. 6. Determined if the two hairs were distinctly separate and recorded observations. 7. Moved the hairs closer together using a dissecting needle and recorded measurements. 8. Determined if the two hairs were distinctly separate and recorded observations. 9. Repeated step 7-8 until the hairs could not be
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
The adult eyeball is about 2.5 cm in diameter. The eyeball is held in place by six extrinsic muscles, which allow the eye to be moved. The front surface of the eye is protected by the eyelids and the eyelashes. The reflex action of 'blinking' protects the surface of the eye. Under the eyelids is a thin transparent layer called the conjunctiva. This is kept moist by secretions from the lachrymal glands (tear glands) which lie above and to the outside of each eye. The fluid contains the enzyme lysozyme which kills bacteria. After passing over the conjunctiva, it drains from the eyes into the nasal cavity. The eyeball has a three layered structure. Structure of the eye Iris - regulates the amount of light entering through the pupil. Iris is a continuation of the choroid. Pigmented, colour of eye. WALL OF EYE IS COMPOSED OF THREE LAYERS: (a) Sclera Sclerotic - outer layer, tough protects and helps maintain shape of eye. White except at front where transparent - called cornea. (b) Choroid - middle layer, vascular, feeds retina cells. In humans, cells contain a black pigment melanin, which prevents light reflection in the eye. (c) Retina - inner layer, light sensitive cells - cones and rods. Fovea (yellow spot) in man only cones found here. Blind spot, retinal absent - where optic nerve leaves eye. Filled by jelly-like vitreous humour containing about 99% water,
The most widely used microscopes are optical microscopes, which use visible light to create a magnified image of an object. The simplest form of optical microscope is the double-convex lens with a short focal length. These lenses can magnify an object by up to 15 times. In general, however, a compound microscope is used, which has multiple lenses to provide more magnification than a single convex lens could alone. Some optical microscopes can magnify an object by 2,000 times or more. The compound microscope consists essentially of two lens systems, the objective and the ocular, mounted at opposite ends of a closed tube. The objective lens is composed of several lens elements that form an enlarged real image of the object being examined. The microscope lenses are set up so that the real image formed by the objective lies at the focal point of the ocular; the observer looking through the ocular sees an enlarged virtual image of the real image. The total magnification of the microscope is determined by the focal lengths of the two lens systems. The accessory equipment of an optical microscope includes a firm stand with a flat stage for holding the material to be examined, and some means for moving the microscope tube towards and away from the stage so that the specimen can be brought into focus. Ordinarily, specimens for microscopic examination are transparent and are viewed by
How does a microscope work?
Liban Ahmed Experiment 1 September 15, 2003 Activity 1: The Microscope Problem How does a microscope work? Hypothesis A microscope enables an individual to see details that are otherwise too small to be seen with the unaided eye by the use of lenses and light to magnify an object. Materials * Prepared slide * Microscope * Microscope slide * Cover slip * Medicine dropper * Lens paper * Newspaper samples from the colored comics and classified ads Procedure Part A-Using the Microscope . Brought a microscope to the lab area making sure to use both hands to carry the microscope and that the cord was not dangling. 2. Looked through the instructions making sure there were no problems that could be posed. 3. Organized the lab area and prepared all equipment including slides and the microscope. 4. Placed the prepared slide on the stage making sure the stage clips held the stage in place. 5. Switched to the low-power objective lens and focused on the image. 6. Recorded observations and calculated magnification. 7. Switched to the medium-power objective lens and focused on the image. 8. Recorded observations. 9. Moved the slide from one side to the other. 0. Recorded observations and calculated magnification. 1. Switched to the high-power objective lens and focused on the image. 2. Recorded
Investigation of the chromatic aberration of a converging lens.
Investigation of the chromatic aberration of a converging lens By Wen Yan Gao Aim To find the difference in focal length of a converging lens when used to produce images with red and blue light. Planning Background information Chromatic aberration arises from dispersion- the property that the refractive index of glass differs with wavelength of light. The focal length of a lens is determined by a combination of its geometry and the refractive index of the material from which it is made. The refractive index varies slightly with the wavelength of the light that is being transmitted. This means that the focal length of a lens will vary for different colours of light. For blue light (short wavelengths), the focal length is larger than that of red light (long wavelengths). Prediction It was predicted that the values of the focal length of the lens obtained from red and blue light are different, given that the standard focal length is 10cm. Proposed Method: The method is to use the lens formula. 1/f = 1/u +1/v To use this formula both the object distance (u) and the image distance (v) need to be measured. This method is not as simple as method 1 above, but the result obtained will be more accurate. Therefore, the focal length of a converging lens in this experiment was determined by method 2. Detailed Procedures: All the lights were switched off to ensure the