OBJECT: To measure the heat of fusion of ice, using the method of mixtures.
METHOD: A piece of ice of known mass is dropped into a calorimeter containing a measured quantity of water. The heat given up by the calorimeter cup and its contents (water, thermometer and stirrer) is computed from their combined thermal capacity and the change in temperature. The heat absorbed by the ice is expressed in terms of the mass of ice, the heat of fusion and the change in temperature of the water from the melted ice. The heat given up by the cup and its contents is set equal to the heat absorbed by the ice, and this equation is solved for the latent heat of fusion. A correction is made for the exchange of heat between the calorimeter cup and its surroundings.
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INTRODUCTION: Experimental work in science is frequently a study of the relationship between two interacting variables. For example the following questions might be answered from experimental data. How does the velocity of a falling body vary with time? What is the angular distribution of radiant energy transmitted through a small opening? What is the pressure response frequency characteristic of a crystal telephone receiver?
When experiments are performed, the independent variable, in these examples time, angle, and frequency, is progressively changed, and the corresponding values of the resulting dependent variable, velocity, intensity, and response respectively, are measured for a series of tests. These data are appropriately recorded in an organized table, that is, in tabular form.
A display of the data as a graph shows more clearly than the tabular form how the one quantity, or property, is related to the second. The graph also indicates probable experimental errors and provides values intermediate to the several readings.
The most powerful form in which the relationship of the variables can be expressed is a mathematical equation. Such equations permit various mathematical expansions and the deduction of additional information. A straight line curve on a graph may be converted quickly to the equation form. Obtaining a straight line curve may require the selection of suitable conversion factors for the axis values, or a special type of graph paper. These techniques, the basis of this discussion, reduce the laborious matching of curves of empirical equations to a reasonable “match” of the original graph form.
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INTRODUCTION: Many experiments are performed to study the manner in which one property or quantity depends upon or varies with another property or quantity. For instance, how does the frictional force between two surfaces vary with the perpendicular force exerted by one surface on the other? Or, how does the length of a pendulum influence its period? Such variables may conveniently be displayed in the form of graphs that summarize the relationships that were studied in the experiment. This discussion will present in an elementary fashion some of the basic ideas connected with the drawing and interpretation of graphs and their use in developing physical laws that express analytically the relationships between the mutually varying quantities.
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