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Grades K–2 · Everyday Life

How does warmth change the liquid level in a thermometer?

A liquid thermometer has a small bulb joined to a narrow tube. The bulb and tube keep the liquid inside. Marks beside the tube form a temperature scale.

J13 visual explanationA schematic sealed, non-mercury liquid thermometer is at 20 degrees Celsius. The liquid expands more than its container on warming, raising the column in the narrow tube; cooling contracts it. The scale is illustrative, no liquid is added, and the diagram has no clinical interpretation.A warmer liquid column risesSchematic non-mercury thermometer · no health reading10°C20°C30°CSame liquidin a narrowsealed tube20°C in this drawn scale; no liquid is added.

In the diagramA warmer liquid column risesSchematic non-mercury thermometer · no health reading10°C20°C30°CSame liquidin a narrowsealed tube20°C in this drawn scale; no liquid is added.

The initial schematic column aligns with 20°C; the same sealed liquid has a lower column at 10°C and a higher column at 30°C.

When this liquid becomes warmer, it takes up more space. It expands more than the container does. The extra space taken by the liquid makes its column rise in the narrow tube. No new liquid is added.

When the thermometer becomes cooler, the liquid takes up less space and the column falls. The narrow tube makes a small change in liquid volume easier to see.

About this explanation

Starting knowledge: Distinguish warmer from cooler and compare higher and lower positions on a picture scale.

Sources

  • National Institute of Standards and Technology — Mercury Thermometer Alternatives: Analog Thermometers
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