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Lesson_1.1 - Lesson 1.1 Temperature and Kinetic Theory of...

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Lesson 1.1 Temperature and Kinetic Theory of Matter. Lesson Objectives: At the end of this lesson students will be able to differentiate between heat and temperature, explain the kinetic theory of gases, interpret the gas laws and use these concepts to solve related problems. Heat is a form of energy and when heat is supplied to an object it increases the internal energy of the object. The internal energy of an object is made up of the kinetic end potential energies of its atoms and molecules. Atoms and molecules have kinetic energy because of their vibrational and translational motion. Potential energy of atoms and molecules are associated with their relative states or positions. When heat energy is supplied to an object, its temperature rises. The rise in temperature is purely due the increase in the translational kinetic energy of the molecules of the object. If the same quantity of heat is supplied to different quantities of water, their increase in temperature will not be the same despite the fact that the total increase in kinetic energy is the same in all cases. The larger quantity will have a smaller increase in temperature while the smaller quantity will have a larger increase in temperature. In case of the larger quantity, more number of molecules share the additional energy, while in the case of the smaller quantity, less number of molecules share the same increase and so the increase in kinetic energy per molecule will be larger in the smaller mass. Therefore, temperature of an object is determined by the average kinetic energy per molecule and not by the total kinetic energy of all the molecules. Temperature of an object is proportional to the average kinetic energy of its molecules .
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While the total internal energy of an object is made up of the potential and kinetic energies of its molecules, its temperature is determined only by the average kinetic energy of its molecules as illustrated in the figure above. 1. Temperature Scales. In order to measure temperature, we make use of properties of materials that change with temperature. For example, most substances expand when heated, and the increase in volume is very nearly proportional to the change in temperature. Therefore, the increase in volume of a substance can be used to measure temperature. Mercury in glass thermometer is an example of this. There are two main scales of temperature used in measuring temperature. One scale called the Celsius scale uses an arbitrary temperature, namely the temperature at which ice melts at atmospheric pressure, as its zero. The other scale called the Kelvin scale uses the temperature at which the molecular energy is zero as its zero. In the Celsius scale, temperature is measured in a unit called degree Celsius ( o C), while in Kelvin scale the unit temperature is a Kelvin (K). We use t to represent temperature in Celsius scale and T for temperature in Kelvin scale.
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