Investigating Science 11–12 · Year 12

Calibrating analogue and digital thermometers at two fixed points

Module 6: Technologies

Practical, model not builtMedium risk

School laboratory, not for home

In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

This site has no interactive model of its own. Where a step or a material names a Concept Studio model, simulation or tool, it has not been built; an external simulation a step names (for example PhET) is not part of this site.

The idea

Every thermometer carries systematic error; checking it at two fixed points, melting ice and boiling water corrected for the day’s air pressure, exposes that error and separates accuracy from resolution.

Safety card

Medium riskA teacher supervises

Setting: In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

Hazards

scalds from steam and boiling water
broken glass thermometer

Controls

clamp the flask; use tongs and heat-resistant gloves
use spirit-filled, not mercury, thermometers
safety glasses

Note

Heat or hot water is used: follow the NSW Department of Education Chemical Safety in Schools (CSIS) package, Section 1, and record a RiskAssess risk assessment before the lesson.

What you need

a liquid-in-glass thermometer (−10 to 110 °C, 1 °C divisions, spirit-filled) and a digital probe thermometer (0.1 °C resolution)
crushed ice and distilled water in a beaker; distilled water in a flask heated on a hotplate, with a stand and clamp
barometer reading, or the station pressure from the Bureau of Meteorology for the school’s location

How to do it

Ice point: stir a slurry of crushed ice and distilled water for 3 minutes and read both thermometers.
Steam point: hold both sensors in the steam just above boiling distilled water and read them once steady.
Record the air pressure and calculate the true boiling point for that pressure.
Calculate each thermometer’s error at both points and write a two-point correction, T_true = a × T_reading + b.
Compare the resolution of each thermometer with its measured accuracy.

What you should see

The ice point is 0.0 °C. From the NIST Antoine equation for water (A = 5.08354, B = 1663.125, C = −45.622, P in bar, T in K) the boiling point is 100.0 °C at 101.325 kPa, 99.6 °C at 100.0 kPa and 98.2 °C at 95.0 kPa. A thermometer reading 99.0 °C in steam on a 100.0 kPa day is therefore 0.6 °C low; a digital probe that shows 0.1 °C steps can still be several tenths of a degree out, which the two fixed points reveal.

What changes

What you change: thermometer type
What you measure: error at each fixed point
What you keep the same: distilled water
sensors not touching the container
pressure recorded at the time

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Water always boils at exactly 100 °C.
More decimal places means more accuracy.
A new thermometer needs no checking.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Investigating Science Stage 6 Syllabus (2017), NESA; currentINS12-13 INS11/12-1 INS11/12-2 INS11/12-4
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

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