Physic Labs

Thermal physics

Temperature and its scales

Read the same temperature on the Celsius, kelvin, and Fahrenheit scales; verify the conversions T(K)=t+273,15T(\mathrm K)=t+273{,}15 and tF=95t+32t_F=\tfrac95 t+32. Use the Celsius slider to inspect the freezing–boiling marks and the sub-0 °C region.

Middle school

Equipment

  • Three virtual thermometers side by side: Celsius / kelvin / Fahrenheit
  • Celsius temperature slider (−100 to 150 °C)
  • Conversion readout T = t + 273.15 K and °F
  • Two fixed marks at 0 °C and 100 °C on the scale

Procedure

  1. Read one temperature on three scales

    Set the slider at 20 °C: the readout shows T=293,15T=293{,}15 K and tF=68,0t_F=68{,}0 °F. Note that K and °C degrees have the same size but different origins — kelvin starts at absolute zero.

  2. Check the fixed points

    Drag to 0 °C and 100 °C — the freezing and boiling marks of water near 1 atm: read 273.15 K / 32 °F and 373.15 K / 212 °F. A 100-degree Celsius span equals exactly 180 Fahrenheit degrees, hence the 9/59/5 factor.

  3. Explore below 0 °C and predict

    Drag down to −40 °C: the point where the C and F scales coincide (tF=tt_F=t). Continue to −100 °C and read T = 173.15 K — kelvin has no negative values. Predict °F at −20 °C with tF=95(−20)+32=−4t_F=\tfrac95(-20)+32=-4 °F and verify.

Simulation

Experiment history

Daniel Gabriel Fahrenheit standardized the mercury thermometer in 1714 and fixed his scale by practical reference points of his era. Anders Celsius proposed the 'hundred-degree' scale in 1742 — initially inverted (boiling = 0, freezing = 100) — reversed after his death, probably by Carolus Linnaeus, into the form we use. In 1848 William Thomson (Lord Kelvin) argued that Carnot's principle implies an absolute temperature scale independent of the working substance — its zero being where an ideal engine reaches maximum efficiency. The international kelvin used the water triple point from 1954; since 2019 the kelvin is defined via the Boltzmann constant.

Related physicists

William Thomson (Lord Kelvin)James Prescott JouleSadi Carnot

Related library topics

Temperature and its scales