Zeroth Law of Thermodynamics

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1 Zeroth Law of Thermodynamics If objects A and B are separately in thermal equilibrium with a third object C, then A and B are in thermal equilibrium with each other.

2 Two objects in thermal equilibrium with each other are at the same temperature.

3 Thermometers and the Celsius Temperature Scale A temperature scale can be established on the basis of any one of these physical properties. On the Celsius temperature scale, this mixture is defined to have a temperature of zero degrees Celsius, which is written as 0 C; this temperature is called the ice point of water. Another commonly used system is a mixture of water and steam in thermal equilibrium at atmospheric pressure; its temperature is 100 C, which is the steam point of water.

4 As a result of thermal expansion, the level of the mercury in the thermometer rises as the mercury is heated by water in the test tube.

5 Kelvin Scale The Kelvin scale is an absolute thermodynamic temperature scale that provides a continuous definition of temperature, valid over all ranges of temperature. Empirical measures of temperature, with different thermometers, can be related to the Kelvin scale. Fahrenheit scale A common temperature scale in everyday use in the United States is the Fahrenheit scale. This scale sets the temperature of the ice point at 32 F and the temperature of the steam point at 212 F.

6 Let p stand for the pressure in a constant-volume gas thermometer in thermal equilibrium with a bath. A value can be assigned to the bath temperature very simply by a linear relation

9 Thermal Expansion of Solids and Liquids Thermal expansion is a consequence of the change in the average separation between the atoms in an object.

10 we define the average coefficient of linear expansion as

13 Heat and Internal Energy Internal energy is all the energy of a system that is associated with its microscopic components atoms and molecules when viewed from a reference frame at rest with respect to the center of mass of the system. Heat is defined as the transfer of energy across the boundary of a system due to a temperature difference between the system and its surroundings. Scientists used to think of heat as a fluid called caloric, which they believed was transferred between objects; thus, they defined heat in terms of the temperature changes produced in an object during heating.

15 The Mechanical Equivalent of Heat Joule s experiment for determining the mechanical equivalent of heat. The falling blocks rotate the paddles, causing the temperature of the water to increase.

17 Conservation of Energy: Calorimetry One technique for measuring specific heat involves heating a sample to some known temperature Tx, placing it in a vessel containing water of known mass and temperature Tw >Tx, and measuring the temperature of the water after equilibrium has been reached. This technique is called calorimetry, and devices in which this energy transfer occurs are called calorimeters.

18 Latent Heat This is the case whenever the physical characteristics of the substance change from one form to another; such a change is commonly referred to as a phase change. Two common phase changes are from solid to liquid (melting) and from liquid to gas (boiling); another is a change in the crystalline structure of a solid.

24 Molar Specific Heat of an Ideal Gas

25 If the molar specific heat is constant, we can express the internal energy of a gas as

28 Adiabatic Processes for an Ideal Gas

30 The heat capacity C of a particular sample of a substance is defined as the amount of energy needed to raise the temperature of that sample by 1 C.

31 The Equipartition of Energy

35 The Molar Specific Heat of Solids

37 Energy Transfer Mechanisms Thermal Conduction Fourier s law

45 Home Insulation In engineering practice, the term L/k for a particular substance is referred to as the R value of the material.

47 convection Newton s law of cooling. Energy transferred by the movement of a warm substance is said to have been transferred by convection. When the movement results from differences in density, as with air around a fire, it is referred to as natural convection. Air flow at a beach is an example of natural convection, as is the mixing that occurs as surface water in a lake cools and sinks. When the heated substance is forced to move by a fan or pump, as in some hot-air and hot-water heating systems, the process is called forced convection.

48 Radiation Stefan Boltzmann law This is known as Stefan s law and is expressed in equation form as

49 The Dewar Flask

50 Un calentador de resistencia eléctrica se encapsula en un cilindro largo de 30 mm de diámetro. Cuando fluye agua con una temperatura de 25ºC y velocidad de 1 m/s cruzando el cilindro, la potencia por unidad de longitud que se requiere para mantener la superficie a una temperatura uniforme de 90ºC es de 28 kw/m. Cuando fluye aire, también a 25ºC, pero con una velocidad de 10 m/s, la potencia por unidad de longitud que se requiere para mantener la misma temperatura superficial es de 400 W/m. Calcule y compare los coeficientes de convección para los flujos de agua y aire.

Lecture 2: Zero law of thermodynamics

Lecture 2: Zero law of thermodynamics 1. Thermometers and temperature scales 2. Thermal contact and thermal equilibrium 3. Zeroth law of thermodynamics 1. Thermometers and Temperature scales We often associate