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📘 How Thermometers Turn Heat Into Numbers

Hold a glass thermometer in your hand and the colored liquid begins a slow climb. Warming makes the liquid expand; the bulb holds much more liquid than the narrow capillary, so a small volume change becomes visible travel. Cooling reverses

3
lessons
~15 min
to learn
Adults
level
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What you’ll learn

  1. Expansion turns warmth into motionExplain how liquid expansion and unequal metal expansion become readable motion.Bulbs, capillaries, and bimetal strips turn warming into movement on a calibrated scale.
  2. Thermocouples turn voltage into temperatureExplain the Seebeck effect, measuring junction, reference junction, and calibration curve.Two unlike metals produce a difference-dependent voltage that electronics interpret.
  3. Infrared sensing reads emitted radiationExplain how emitted infrared, emissivity, and field of view affect noncontact readings.Infrared instruments estimate surface temperature from incoming radiation and calibration assumptions.

Questions this course answers

Why does liquid rise visibly in a thermometer?

The liquid expands when warmed, and the narrow tube converts a small volume change into visible movement.

What creates the useful thermocouple voltage?

The Seebeck effect produces a voltage related to the temperature difference and the metal pair.

Why can a shiny metal surface mislead an infrared thermometer?

Infrared instruments infer surface temperature from radiation, and the inference depends on emissivity and the viewed scene.

Grounded in trusted sources

  • NIST, Mercury Thermometer Alternatives: Thermocouple, https://www.nist.gov/pml/sensor-science/thermodynamic-metrology/mercury-thermometer-alternatives/mercury-thermometer-5
  • NIST, Precise Temperature Measurements with Invisible Light, https://www.nist.gov/news-events/news/2019/05/precise-temperature-measurements-invisible-light
  • BIPM, SI unit: kelvin, https://www.bipm.org/en/si-base-units/kelvin
  • NIST, Thermometry, https://www.nist.gov/programs-projects/thermometry
  • NIST, Thermocouples Calibrations Services, https://www.nist.gov/pml/sensor-science/temperature-humidity/thermocouples-calibrations-services
  • Wikimedia Commons MediaWiki API, image metadata and thumbnails, https://commons.wikimedia.org/w/api.php

Every Wunder lesson is built from real, reputable sources — never invented.

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