Thermodynamics
Temperature scales, thermal expansion, heat & calorimetry, ideal gas laws, kinetic theory, and the first law of thermodynamics — the physics that governs energy, heat, and molecular motion.
University of Szeged · Department of Medical Physics & Informatics · v2.3
Temperature & Temperature Scales
Temperature is the property that determines whether an object is in thermal equilibrium with others. When two objects are at the same temperature, there is no net heat transfer between them. It is NOT the same as heat — a metal ice-tray and a cardboard box in the same freezer are the same temperature, yet the metal feels colder because it conducts heat away from your hand faster.
Thermometers & Measuring Temperature
Thermometers exploit a physical property that changes with temperature: liquid volume (mercury/alcohol), gas pressure, electrical resistance, or color (IR thermometers). All rely on the principle that the measuring device reaches thermal equilibrium with the object being measured.
Three Temperature Scales
Celsius (°C)
0°C = ice melts
100°C = water boils
Most widely used worldwide.
Kelvin (K)
0 K = absolute zero (−273.15°C)
Same degree size as Celsius
SI unit. Used in gas laws & physics.