PX154 - B1 - heat and temperature

[YF17]

temperature

• a physical property related to the kinetic energy of the atoms, molecules and/or electrons of the system under study
  • this energy is the "internal energy" of the system, given the symbol $U$

temperature scales

• we need some observable property that changes predictably with temperature
  • eg: mercury/alcohol based thermometers, thermocouples, infrared measurements, behaviour of ideal gases (using $pV=NRT$)
• ideally, we want a linear dependence of the property on temperature:
  • $X(T)=X_0+cT$
    • where, $X_0=$ value at some temperature, $cT=$ some constant
    • let's use two fixed points:
      • eg:
        • ice point (freezing/melting of pure water)
        • steam point (boiling point of pure water - mix of water/gas)
      • set:
        • ice point $=0\mathrm{°}C$
        • set steam point $=100\mathrm{°}C$
      • we can use these two fixed points to calibrate our thermometer
        
      • $T(X)=100\frac{X-X_1}{(X_2-X_1)}$