In general, pipets are used to measure and transport very precise volumes of liquids between containers or solutions. The term micropipet is used to describe a pipette that is used to work with very small volumes, less than 1000 ul (1 ml). Research assistants, scientists, and medical laboratory workers are just some of the professionals that utilize pipets in their laboratories.
There are almost countless makes and models of micropipets. Some of the functional features that may differ between models include volume range, incremental units, mode of operation (electronic or mechanical), autoclavability, and various ergonomic design features. To choose a model that is best for your laboratory and the proposed activity it is important to consider these features.
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OBJECT: To make an experimental determination of the mechanical equivalent of heat using a continuous flow calorimeter.
METHOD: A stream of water flowing through a glass tube is heated by an electric current passing through a heating element contained in the tube. The temperature difference between the water entering and leaving the tube depends upon the amount of energy supplied per unit time to the heating element (power input) and upon the mass of water flowing through the tube per unit time. A uniform rate of flow of water is maintained and several determinations of the temperature difference are made for corresponding values of the power input. From the measured rate of flow and the slope of a graph of power input versus temperature difference, the value of the mechanical equivalent of heat is determined.
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OBJECT: To study the properties of a compound pendulum, and to determine the acceleration due to gravity by the use of such a pendulum.
METHOD: An experimental pendulum is suspended successively about several axes at different points along its length and the period about each axis is observed. A graph is plotted of the period versus the distance of the axis of suspension from one end of the pendulum. The nature of the graph shows the physical properties of the compound pendulum. From values of the period and the corresponding length of the equivalent simple pendulum as determined from the graph, the acceleration due to gravity is calculated. From the mass of the pendulum and its radius of gyration as obtained from the curve, the rotational inertia of the pendulum is computed.
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OBJECT: To determine by means of vector diagrams the resultant of several concurrent forces and to check the accuracy of the result on a force table.
METHOD: Each student is assigned a problem. In this problem it is assumed that the magnitude and direction of certain forces acting on a body are known. The resultant and anti-resultant (equilibrant) of these given forces are determined both by graphical method and by the use of trigonometric relationships. The accuracy of the result is checked on a force table.
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OBJECT: To study the composition and resolution of concurrent forces as examples of vector quantities.
METHOD: Concurrent forces acting on a body are used as examples of vector quantities. These forces are represented by vectors. The resultant and equilibrant of several sets of such known forces are determined by both graphical and analytical methods. These results are tested on a force table as a check on the first condition for the equilibrium of a rigid body.
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