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Measurement of Temperature is taught in the note for Temperature. Read it below and look for the section on this topic.

Temperature

8 min read

Temperature and heat

Temperature tells us how hot or cold something is. It is related to the average kinetic energy of its particles: the hotter the object, the faster its particles move. Heat is energy that flows from a hotter object to a colder one. Heat is measured in joules; temperature in degrees Celsius (°C) or kelvin (K).

Thermometers and scales

A liquid-in-glass thermometer works because the liquid expands as it is heated. It is calibrated with two fixed points: the lower fixed point (ice point, 0 °C, the temperature of pure melting ice) and the upper fixed point (steam point, 100 °C, the temperature of steam above boiling pure water at normal pressure). The space between is divided into 100 equal steps.

Fixed points of a thermometerA thermometer in melting ice reads 0 degrees Celsius, the lower fixed point. A thermometer in the steam above boiling water reads 100 degrees Celsius, the upper fixed point. The space between is divided into 100 equal parts.melting icelower fixed point 0 °Csteam above boiling waterupper fixed point 100 °C100 equal steps
ThermometerLiquid / deviceGood for
Mercurymercurywide range, accurate
Alcoholcoloured alcoholvery low temperatures
Clinicalmercury with a kinkbody temperature (35 – 42 °C)
Digitalelectronic sensorquick readings
Kelvin = Celsius + 273. The graph is a straight line: every 1 °C step is also a 1 K step, so the scales are the same size but start in different places.
0 K (absolute zero) is the lowest possible temperature, about −273 °C.
Try itRead the thermometer

Change the temperature and watch the liquid rise. Notice the kelvin value.

Worked exampleConvert

Normal body temperature is 37 °C. Express it in kelvin.

  1. Add 273.

Answer: 310 K

Check yourself Which temperature is the steam point of water?
Check yourself Convert 300 K to °C.

Key terms

Temperature
How hot something is; related to the average kinetic energy of its particles.
Heat
Energy transferred because of a temperature difference.
Fixed points
Reference temperatures used to calibrate a thermometer.

Summary

  • Temperature measures hotness; heat is energy transferred.
  • Thermometers use fixed points: ice point 0 °C and steam point 100 °C.
  • T(K) = θ(°C) + 273.
Concept of Temperature