5. How a Laboratory Thermometer Works (Function / Principle)

Basic Principle:

A lab thermometer works on the thermal expansion of liquids.

When the thermometer is heated:

• Mercury/alcohol in the bulb expands

• It rises through the capillary tube

• The temperature is read on the scale

When cooled:

• The liquid contracts

• It moves down the tube

• Lower temperature is indicated

This principle is called “thermal expansion.”

6. Functions / Uses of a Laboratory Thermometer

A laboratory thermometer is used to:

1. Measure temperature of chemical reactions

2. Monitor heating of solutions

3. Measure boiling and melting points

4. Study temperature changes in physics experiments

5. Check the temperature of laboratory equipment

6. Conduct calibration and standardization work

7. Important Features of a Laboratory Thermometer

• Narrow capillary tube for precise readings

• No constriction (unlike clinical thermometers)

• Fast response to temperature changes

• Double scale (°C and °F) in some models

• Made of heat-resistant glass

8. Precautions While Using a Laboratory Thermometer

• Do not use a mercury thermometer with cracked glass.

• Keep the thermometer vertical while reading.

• Do not hold the bulb with your hand (affects reading).

• Avoid sudden temperature changes—glass may break.

• Read at eye level for accuracy.

Summary Table