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