Chapter 21 Temperature
Chapter 21 Temperature
21-1 Temperature and thermal equilibrium 1. Thermal equilibrium (a) Adiabatic(绝热)( thermally insulating) Fig 21-1 shows two systems A and b, they are isolated from one another and from their environment by which A B we mean that neither energy nor matter can enter or leave either system Fig 21-1
21-1 Temperature and thermal equilibrium 1. Thermal equilibrium (a) Adiabatic(绝热) ( thermally insulating ) Fig 21-1 shows two systems A and B, they are isolated from one another and from their environment, by which we mean that neither energy nor matter can enter or leave either system. Fig 21-1 A B TA TB
For example, the systems may be surrounded by WQl∥ made of thick slabs of styrofoam(泡沫聚苯乙烯 (b) Diathermic(热透性) means thermally conducting (c Thermal equilibrium When the two system are placed in contact through a diathermic wall, the passage of heat energy through the wall causes the properties of
For example, the systems may be surrounded by wall made of thick slabs of styrofoam(泡沫聚苯乙烯). (b) Diathermic(热透性), means thermally conducting (c) Thermal equilibrium When the two system are placed in contact through a diathermic wall, the passage of heat energy through the wall causes the properties of
two system to change. The changes goes to until finally all measured properties of each system approach constant values. When this occurs, we say that the two systems are in thermal equilibrium with each other 2. Zeroth law of thermodynamics If system a and b are each in thermal equilibrium with a third system C, then a and b are in thermal equilibrium with each other
two system to change. The changes goes to until finally all measured properties of each system approach constant values. When this occurs, we say that the two systems are in thermal equilibrium with each other. 2. Zeroth law of thermodynamics “If system A and B are each in thermal equilibrium with a third system C, then A and B are in thermal equilibrium with each other
The zeroth law underlies the concept of temperature 3.Temperature When two system are in thermal equilibrium we say that they have the same temperature
The zeroth law underlies the concept of temperature . 3. Temperature When two system are in thermal equilibrium we say that they have the same temperature
21-2 Temperature Scales(温标) Three temperature scales are defined Kelvin scale, Celsius scale. and Fahrenheit scale 1.Kelvin scales(7) The definition: The triple point(三相点) of water was set to be(in 1954) 7=273.16K It is one of the seven base units of sI Units Although there is no apparent limit to how high the temperature of a system can be there is a limit to how low it can be. T>0K
21-2 Temperature Scales （温标） 1. Kelvin scales (T) • The definition: The triple point (三相点) of water was set to be (in 1954): • It is one of the seven base units of SI Units. • Although there is no apparent limit to how high the temperature of a system can be, there is a limit to how low it can be. T > 0 K Ttr = 273.16 K Three temperature scales are defined: Kelvin scale , Celsius scale, and Fahrenheit scale
2 Celsius and fahrenheit scales (a celsius scale(the centigrade scale The normal freezing point of water is defined to beo c The normal boiling paint of water is defined to be 100c The triple point of water is found to be 0.01c(27316K) T-273.15 (21-2) (b)Fahrenheit scale Tn=-T+32 (21-3) T=25C T=77°F TC=38CTF=100°F
2. Celsius and Fahrenheit scales (a) Celsius scale (the centigrade scale ): The normal freezing point of water is defined to be ; The normal boiling point of water is defined to be . The triple point of water is found to be (273.16K). (21-2) (b) Fahrenheit scale (21-3) c 0 c 100 32 5 9 TF = TC + TC = T − 273.15 c 0.01 TC=25 c TF=77 F TC=38 c TF=100 F
21-3 Measuring temperatures Based on Kelvin scale 1. Any property of a substance that varies with temperature of the system can form the basis for a thermometer(温度表) T usually is some function of x, thermometric property. f(x) The simplest way is to choose linear relationship between T and x T=ax 21-5 Where a is a constant
21-3 Measuring temperatures Based on Kelvin scale. 1.Any property of a substance that varies with temperature of the system can form the basis for a thermometer(温度表). •T usually is some function of x, thermometric property. T* = f(x) •The simplest way is to choose linear relationship between T and x: , * T = ax (21-5) where a is a constant
The constant 'a can be obtained by measuring x at the triple point of water. If it is xir at 27316K, we have T273.16 孓 T(x)=273.16K (21-6) We express temperature in eq(21-5)by T*rather than T because the temperature so measured will be a device sensitive temperature, not a universal one
•The constant ‘a’ can be obtained by measuring x at the triple point of water. If it is at 273.16K, we have • We express temperature in Eq(21-5) by T* rather than T because the temperature so measured will be “a device sensitive temperature”, not a universal one. tr x t r x x T (x) 273.16K * = tr x x T a 273.16 * = = (21-6)
Sample problem 21-1 The resistance of a certain coil of platinum wire increases by a factor of 1. 392 between the triple point of water and the boiling point of water at atmospheric pressure. What temperature for the normal boiling point of water is measured by this thermometer? Solution: T(Rhou)= roily (273.16(1.392)=3802K R This value gives"platinum resistance temperature" of boiling water. Other thermometers will give different values
Sample problem 21-1 The resistance of a certain coil of platinum wire increases by a factor of 1.392 between the triple point of water and the boiling point of water at atmospheric pressure. What temperature for the normal boiling point of water is measured by this thermometer? Solution: K R R T R T t r boil ( boil) t r (273.16)(1.392) 380.2 * = = = This value gives “platinum resistance temperature” of boiling water. Other thermometers will give different values
