Hvilket er en grund til, at termometre mister nøjagtighed?
Mercury-in-glass thermometer
For at kalibrere termometeret bringes pæren i termisk ligevægt med en temperaturstandard, f.eks. en is/vand-blanding, og derefter med en anden standard, f.eks. vand/damp, og røret opdeles i regelmæssige intervaller mellem de faste punkter. I princippet kan man forvente, at termometre af forskellige materialer (f.eks. farvede alkoholtermometre) vil give forskellige mellemliggende aflæsninger på grund af forskellige ekspansionsegenskaber; i praksis vælges de anvendte stoffer således, at de har rimeligt lineære ekspansionsegenskaber som funktion af den sande termodynamiske temperatur, og de giver således lignende resultater.
Mercury-in-glass thermometer
In order to calibrate the thermometer, the bulb is made to reach thermal equilibrium with a temperature standard such as an ice/water mixture, and then with another standard such as water/vapour, and the tube is divided into regular intervals between the fixed points. In principle, thermometers made of different material (e.g., coloured alcohol thermometers) might be expected to give different intermediate readings due to different expansion properties; in practice the substances used are chosen to have reasonably linear expansion characteristics as a function of true thermodynamic temperature, and so give similar results.
Mercury-in-glass thermometer