Methodology, Techniques, and History, Part 2
Question 1: Describe light microscopes.
Answer 1: There are different kinds of microscopes, but optical or light microscopes are the most commonly used in lab settings. Light and lenses are used to magnify and view samples. A specimen or sample is placed on a slide and the slide is placed on a stage with a hole in it. Light passes through the hole and illuminates the sample. The sample is magnified by lenses and viewed through the eyepiece. A simple microscope has one lens, while a typical compound microscope has three lenses. The light source can be room light redirected by a mirror or the microscope can have its own independent light source that passes through a condenser. In this case, there are diaphragms and filters to allow light intensity to be controlled. Optical microscopes also have coarse and fine adjustment knobs.
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Question 2: Detail how to prepare slides and use a light microscope.
Answer 2: Wet mount slides designed for use with a light microscope typically require a thin portion of the specimen to be placed on a standard glass slide. A drop of water is added and a cover slip or cover glass is placed on top. Air bubbles and fingerprints can make viewing difficult. Placing the cover slip on at a 45 degree angle and allowing it to drop into place can help avoid the problem of air bubbles. A cover slip should always be used when viewing wet mount slides. The viewer should start with the objective in its lowest position and then fine focus. The microscope should be carried with two hands and stored with the low-power objective in the down position. Lenses should be cleaned with lens paper only. A graticule slide is marked with a grid line, and is useful only for counting or estimating a quantity.
Question 3: List the main types of balances and describe their parts.
Answer 3: Unlike laboratory glassware that measures volume, balances such as triple-beam balances, spring balances, and electronic balances measure mass and force. An electronic balance is the most accurate, followed by a triple-beam balance and then a spring balance. One part of a triple-beam balance is the plate, which is where the item to be weighed is placed. There are also three beams that have hatch marks indicating amounts and hold the weights that rest in the notches. The front beam measures weights between 0 and 10 grams, the middle beam measures weights in 100 gram increments, and the far beam measures weights in 10 gram increments. The sum of the weight of each beam is the total weight of the object. A triple beam balance also includes a set screw to calibrate the equipment and a mark indicating the object and counterweights are in balance. Analytical balances are accurate to within 0.0001 g.
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