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 constant21-3 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