Temperature Scales and Kelvin Conversions

  • Temperature and thermometer basics
    • Temperature measures hotness/coldness; liquids in a glass thermometer expand with heat, allowing measurement.
    • Reference values are used to mark scales: freezing and boiling of water at 1 atm.
  • Reference temperatures and scale intervals
    • Celsius scale (1.0 atm)
    • Freezing: 0∘C0^{\circ}\mathrm{C}
    • Boiling: 100∘C100^{\circ}\mathrm{C}
    • Interval: 100100 degrees
    • Fahrenheit scale (1.0 atm)
    • Freezing: 32∘F32^{\circ}\mathrm{F}
    • Boiling: 212∘F212^{\circ}\mathrm{F}
    • Interval: 180180 degrees
    • Note: Celsius and Kelvin have degrees of the same magnitude; Fahrenheit degrees are different in size.
    • Therefore, Celsius–Fahrenheit conversions must account for the difference in magnitude.
  • Celsius ↔ Kelvin relationship
    • The SI unit of temperature is the kelvin (K).
    • A degree Celsius is the same size as a kelvin: one can shift between scales by a constant offset.
    • Convert Celsius to Kelvin: T<em>K=T</em>C+273.15T<em>K = T</em>C + 273.15
    • Convert Kelvin to Celsius: T<em>C=T</em>K−273.15T<em>C = T</em>K - 273.15
  • Kelvin: absolute temperature scale
    • 0 K corresponds to absolute zero (theoretical lowest temperature).
    • Origin: based on gas-volume–temperature relationship; proposed by Lord Kelvin (William Thomson) in 1848.
    • Although Kelvin is the official SI scale, Celsius remains widely used in scientific and many other contexts.
  • Practical usage and global context
    • Celsius is the common scale for most scientific contexts and daily life globally.
    • Fahrenheit is still used in the United States and a few territories (e.g., Bahamas, Belize, Cayman Islands, Palau) for weather, medicine, and cooking.