Parts of a Thermometer

A glass thermometer drawn wide enough to see inside, and a digital one beside it.

Parts of a Thermometer

Name Date

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1 2 3 4 5 6 7 8 9
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Write the name of each numbered part.Answer key

  1. Bulb
  2. Scale
  3. Stem
  4. Liquid column
  5. Display
  6. Probe
  7. Capillary bore
  8. Meniscus
  9. Expansion chamber

Own drawing from plain geometry. Licence: own work.

Each numbered ring is a button. Use the arrow keys to move between them and Enter to choose. Names are read out in Study, and once a part is answered.

Next step Next: read the marks on a ruler

All 9 parts on the diagram

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Liquid-in-glass 7

  1. Bulb The reservoir that holds most of the liquid.
  2. Scale The lines the temperature is read against.
  3. Stem The glass tube that carries the bore and the scale.
  4. Liquid column The thread of liquid. It lengthens as it warms.
  5. Capillary bore The very fine channel the liquid rises in.
  6. Meniscus The top of the liquid. Its position gives the reading.
  7. Expansion chamber An enlargement at the top end of the bore.

Digital 2

  1. Display Shows the temperature as a number.
  2. Probe The sensing end. It is put into what is measured.

How this list was compiled: Every name checked on 2026-09-30 and kept only where at least two of these use it. (1) US National Bureau of Standards, Monograph 150, Liquid-in-Glass Thermometry (1976), a US federal work, full text at https://archive.org/details/liquidinglassthe150wise_0 : bulb (the reservoir for the liquid), stem, capillary bore, main scale, liquid column, meniscus, expansion chamber (an enlargement at the top end of the capillary bore). (2) Wikipedia, Thermometer, Mercury-in-glass thermometer and Alcohol thermometer, https://en.wikipedia.org/wiki/Mercury-in-glass_thermometer and https://en.wikipedia.org/wiki/Alcohol_thermometer : bulb, stem, capillary bore, scale, the meniscus whose position shows the temperature, the expansion bulb that seals the end, a temperature sensor and a digital display. (3) and (4) two makers' manuals for digital thermometers, names only, full texts at https://archive.org/details/manualzilla-id-6193881 and https://archive.org/details/manualzilla-id-6723438 : probe, display. Licence: own work

The drawing: Own drawing from plain geometry; nothing traced. Licence: own work

How it works

A thermometer has a part that senses temperature and a part that shows it. In a glass thermometer those are the bulb and the scale on the stem. In a digital one they are the probe and the display.

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The glass thermometer

The bulb holds the liquid. When it warms, the liquid expands up the capillary bore, a very fine channel in the stem. The top of the liquid column, the meniscus, is read against the scale.

The digital thermometer

The probe is the sensing end. The display shows the temperature as a number.

  • The glass thermometer is drawn much wider than a real one, so the bore and the liquid in it can be seen.

Questions and answers

What are the parts of a thermometer called?

On a liquid-in-glass thermometer: the bulb, the stem, the capillary bore, the liquid column with its meniscus, the scale and the expansion chamber. On a digital thermometer: the probe and the display.

What is the bulb of a thermometer for?

It is the reservoir for the liquid, and the part that senses the temperature. As the liquid in the bulb warms it expands, and the extra volume moves up the bore.

What is the liquid in a glass thermometer?

Mercury or an alcohol. Both expand as they warm and contract as they cool, which moves the top of the column along the scale.

What is the expansion chamber in a thermometer?

A small enlargement at the top end of the capillary bore. In a gas-filled thermometer it keeps the pressure from building up as the liquid nears the top of the scale.

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