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Title: The Microscope And Its Use
To learn how to identify the parts of the compound microscope.
To learn the way of cleaning the lenses.
To learn the method of viewing a prepared slide.
To learn the basic in computing magnification.
To learn the steps in measuring objects in the microscope.
To learn the procedure in preparing a wet mount.
A binocular compound light microscopeA slide
Special lens paperA teasing needled
A prepared slideA coverslip
A ruler Onion
- Identifying The Parts
Interpupillary Distance (Interocular Distance)
Reading on the interocular scale:
Interocular scale reading: 65 mm
- Viewing A Prepared Slide
- Now look through the microscope and adjust the diaphragm lever (and condenser knob) so that enough light is coming through to make the field bright. In which direction do you move the lever to increase the amount of light?
I will move the lever in a clockwise direction.
- View the objective lens from the side and turn the coarse adjustment until the lens almost touches the slide. Do you turn the knob towards you or away from you?
I will turn the knob away from me.
- Finish focusing the fine adjustment knob. Does the object appear normal or upside down?
The image of the object will appears upside down.
- Move the slide a tiny bit away from you while observing the object in the microscope. Does it move away from you or towards you?
The object in the microscope will move towards me.
- Computing Magnification
- Measuring Objects In The Microscope
If the field of view is a certain size under the lowest power or magnification, it will be correspondingly smaller as the power is increased. If the magnification is known, the relative sizes of the two fields can be calculated.
- Place a ruler on your stage and measure the size of the field under the lowest magnification:
Lowest total magnification = 40x
- Switch to another magnification:
Total magnification = 100x
- The diameter of the visual field for the high-power objective (40x) can be computed by using the following formula:
M1 F1 = M2 F2
Where M1 = magnification of lower-power objective (4x)
M2 = magnification oh high-power objective (40x)
F1 = diameter of visual field at low magnification; and
F2 = diameter of visual field at high magnification
Organism measured: Onion cell (Alium cepa)
Objective lens at low-power (M1): 4x
Objective lens at high-power (M2): 40
Size of field: M1 F1 = M2 F2
(4)(4) = 40 (F2)
F2 = 0.4mm
Relative size of an organism: 0.4/8 = 0.05mm
Size of organism (µm): 50
- Preparing A Wet Mount
- Locate your organism under low power and then switch to high power. Make a sketch of what you observe, and record the total magnification.
Total Magnification = 400x
Using the visual field as a guide, estimate the size of the organism; 0.4/6 = 67 µm
Identify the organism if you can: Onion cell
A sketch of the onion cell:
The compound microscope is light illuminated. It is commonly used to view living things with single cell layer, cells and tissues. The image seen from this microscope is two dimensional and colored. It is helpful in enhancing our ability to see details by 1000 times. It even allows us to view objects that are as small as 0.1 micrometer or 100 nanometers. The resolution of this microscope is limited due to the wavelength of the light, which ranges from about 400 to 700 nanometers. The power of the eyepiece is usually 10x and the power of objectives are 4x, 10x, 40x and 1000x. To get the total magnification, times the power of eyepiece and objectives to obtain 40x, 100x, 400x and 1000x respectively. Hence, compound microscope has a low resolution but a high magnification. The two hollow cylinders in the compound microscope contains two double convex lenses. One of the lens, the objective lens, is fixed near to the specimen (to collect light) will formed a real, inverted image at a point on the principal focus of the upper lens, the eyepiece in the microscope. The second lens, the eyepiece then magnifies the image, giving an enlarged inverted virtual image of the object, allowing the eyes to observe.
Electron microscope is a type of microscope that uses transmitted electrons controlled by electric or magnetic fields to create an image of a specimen. It is not limited by the powers of the optical lenses and the presence of light source. The wavelength of an electron can be up to 100,000 times shorter than of visible light photons. Hence, providing a greater magnification and depth of focus, revealing more details of the specimens compare to a normal light microscope. This specialty helps to extend our viewing ability much further.
The electron microscope can be classified inti two types. One is the Transmission Electron Microscope (TEM) and another one is the Scanning Electron Microscope (SEM). TEM utilizes energetic electrons to yield information and details on element and compound structure. The maximum potential magnification of TEM is around 0.1 nanometer and high resolution. This provides us the ability to obtain information of surface features, shapes and sizes. Hence, it is considered as an impressive instrument that provides high-quality, detailed and two-dimensional images. This microscope ability allows a wide range of science, education and industry applications. It is also useful in the study of crystals and metals Experiments that uses TEM is conducted in a vacuum chamber as electrons are deflected by particles in the air,. However, TEM is large and expensive, which only provides black and white images. Skills are also required to prepare specimens. It requires a specially designed room with services such as magnetic field cancelling system. This is because TEM is sensitive to vibration and electromagnetic fields and must be kept from exposure, in isolation.
Scanning Electron Microscope(SEM) also uses focused beams of electrons to obtain specimen’s information. SEM provides high resolution and three-dimensional images with topographical, morphological and compositional information which is highly used for science and industry applications and capabilities. It provides detailed surface date of solid specimens with a maximum magnification of about 100000x. This instrument works fast and the generation of data is shown in digital form (technological advances). Same as TEM, experiments are conducted in vacuum chamber. It is only limited to solid, inorganic samples which are only able to fit into the vacuum chamber. SEM is expensive and must be placed in a place free of any possible magnetic or vibration interference. Besides that, maintenance such as keeping a steady voltage, currents to electromagnetic coils and circulation of cool water are required.
Stereozoom microscope is a microscope that normally uses reflected visible light to illuminate the surface of a specimen. Hence, it is used widely for manufacture and inspection in manufacturing industries. The magnification is typically low, at a range from 10x to 80x. The exact magnification is required in order to view the details of the specimen. To overcome poor illumination or resolution, a higher magnification is often used. Another two important qualities for this microscope is the depth of field and the working distance, which are inversely related to resolution. With a higher resolution, the smaller the depth and working distance is needed. There are two optical paths that transfer the image of the object from the eyepiece all the way to the final objective lens, providing a perception of a three-dimensional view. This happens as we view the specimen from two slightly different angles, giving us a more accurate visual of the specimen’s surface, unlike other microscopes which have to be viewed from an upright position.
The parts of the microscope is successfully identified.
The process of cleaning the lenses is successfully done.
The prepared slide has been successfully viewed under the microscope.
The computation of magnification is successfully recorded.
The objects in the microscope has been successfully measured.
The process of preparing a wet mount is successfully done.
II. Use Of The Streozoom Microscope
Questions (Viewing Specimens):
- What is the magnification range of this microscope (stereozoom microscope)?
10x – 65x
- Is the image of the specimen inverted as in the compound microscope?
- Describe the type of illumination used by your microscope. Is there a choice?
The types of illumination are reflected light, combination light and transmitted light.
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