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Measure temperature · Biology · Chemistry · Physics

Thermometer

Thermometer, with labels: bulb, liquid column, scale in °C.

What it is for

A thermometer measures how hot something is. The liquid in the thin tube expands as it warms and rises up the scale; the temperature is where the liquid stops.

Range
–10 °C to 110 °C (the Practical Test thermometer)
Smallest division
1 °C
Record to
the nearest 0.5 °C, e.g. 24.5 °C

Why choose it

For the temperature of a liquid: water in a beaker, a reaction in a polystyrene cup, a water bath for enzymes. A digital thermometer or temperature probe may show 0.1 °C, and with a data logger it takes many readings in a row; check what its display resolves.

How to read it

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  1. In a liquid, put the bulb fully in, clear of the bottom and sides; in a metal block, put it in the thermometer hole.
  2. Stir a liquid. Wait for a steady reading; when heating or cooling, read at the stated times; in a reaction, note the highest (or lowest) value.
  3. Keep your eye level with the top of the liquid column.
  4. Read to the nearest half division and write the unit: 24.5 °C.

Exam-style question

A student puts 25 cm³ of hydrochloric acid in a polystyrene cup and adds sodium hydroxide solution. The thermometer shows 21.0 °C before mixing and 27.5 °C after.

  1. Calculate the temperature change.
  2. Is the reaction exothermic or endothermic? Explain.
  3. Why is a polystyrene cup used instead of a glass beaker?
Show what a good answer says
  1. 27.5 − 21.0 = 6.5 °C, a rise.
  2. Exothermic: the temperature rises because the reaction gives out energy to the mixture and its surroundings.
  3. Polystyrene is a poor conductor of heat (an insulator), so less energy escapes and the measured rise is closer to the true one.

Teaching points for checking your own answer, not official Cambridge marks.

Common errors

  • Reading from above or below the top of the liquid (parallax error), not with your eye level with it.
  • Reading a steady liquid before the value has stopped changing, or missing the highest temperature of a reaction.
  • Letting the bulb rest on the bottom or side: near a hotplate or flame it then shows the glass, not the liquid.
  • Writing more figures than the scale gives (24.37 °C), or leaving out °C.

Where you use it here

From the Practical Test apparatus lists of the Cambridge IGCSE Biology 0610, Chemistry 0620 and Physics 0625 syllabuses for 2026–2028, and the apparatus the experiments on this site use.

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