General Physics(ppt) Ch 18

General Physics(ppt) Ch 18 - 18 Temperature Heat and the...

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Unformatted text preview: 18 Temperature, Heat, and the First Law of Thermodynamics s One of the principal branches of physics and engineering is thermodynamics ( 熱力學 ), which is the study and application of the thermal energy 1 (internal energy) of systems. s One of the central concepts of thermodynamics is temperature , which we begin to explore. s Temperature is one of the seven SI base quantities. Physicists measure temperature on the Kelvin scale (in units called kelvins ). Although the temperature o a Temperature 2 s Although the temperature of a body apparently has no upper limit, it does have a lower limit; this limiting low temperature is taken as the zero of the Kelvin temperature scale . s Room temperature is about 290 kelvins, or 290 K , above this absolute zero (0 K). T room (290K) The Zeroth Law of Thermodynamics 3 測溫器 測溫器 測溫器 測溫器 ( 熱感應元件 ) Fig.18-3 (a) Thermoscope T and A are in thermal equilibrium ( 熱平衡 ). (S is a thermally insulating screen.) (b) T and B are also in thermal equilibrium , at the same reading S 4 of the thermoscope. (c) If (a) and (b) are true, the zeroth law of thermodynamics states that A and B are also in thermal equilibrium . s The experimental fact shown in Fig. 18-3 is summed up in the zeroth law of thermodynamics : If bodies A and B are each in thermal equilibrium with a third body T, then A and B are in thermal equilibrium with each other. 5 s In less formal language, the message of the zeroth law is: “Every body has a property called temperature . When two bodies are in thermal equilibrium, their temperatures are equal. And vice versa.” s If T represents a Celsius ( 攝氏 ) temperature C and T a Kelvin temperature, then The Celsius and Fahrenheit Scales 6 s The relation between the Celsius (T c ) and Fahrenheit ( 華 氏 ) (T F ) scales is 7 Thermal Expansion s If the temperature of a metal rod of length L is raised by an amount Δ T, its length is found to increase by an Linear Expansion 8 amount in which α is a constant called the coefficient of linear expansion ( 線膨脹係數 : 每升高 Δ T ,長度增長 比例 Δ L/L). 9 混凝土 黃銅 鎳鐵合金 s We describe the coffee as a system (with temperature T s ) and the kitchen as the environment (with temperature T E ) of that system. Our observation is that if T s is not equal to T E , then T s will change (T E can also change some unt T =T and thu therma equilibrium Temperature and Heat T s T E Kitchen (environment) Coffee (system) 10 change some) until T E =T s and thus thermal equilibrium is reached. s Such a change in temperature is due to a change in the thermal energy of the system because of a transfer of energy between the system and the environment. The transferred energy is called heat and is symbolized Q ....
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This note was uploaded on 12/27/2011 for the course LSCI 103 taught by Professor K.y.liao during the Fall '11 term at National Cheng Kung University.

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General Physics(ppt) Ch 18 - 18 Temperature Heat and the...

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