# Thermometry & Thermometric Property

Show/Hide Sub-topics (Thermal Physics | O Level Physics)
Show/Hide Sub-topics (Thermal Physics | A Level Physics)

## Thermometry

Thermometry (Aka. temperature measurement) is essential to a wide range of activities, including manufacturing, scientific research, and medical practice. The ability to measure temperature accurately was only developed recently.

For accurate readings, thermometer must be much smaller than the system, so that the energy the thermometer gains or loses does not significantly alter the energy content of the system.

Thermometer can be calibrated by placing them in thermal contact with environments that remain at constant temperature. Eg. Pure melting ice(0°C) and pure boiling water (100°C) at 1 ATM.

Fun Fact:
Galileo invented the first thermometer. In his instrument, the changing temperature of an inverted glass vessel produced the expansion or contraction of the air within it, which in turn changed the level of the liquid with which the vessel’s long, open-mouthed neck was partially filled. This general principle was perfected in succeeding years by experimenting with liquids such as mercury and by providing a scale to measure the expansion and contraction brought about in such liquids by rising and falling temperature.

## Thermometric Property

An instrument, a thermometer, is required to measure temperature objectively. The thermometer makes use of a physical property of a thermometric substance which changes continuously with temperature. The physical property is referred to as thermometric property.

## Thermometric Properties Used In Various Thermometers

The following table shows some of the thermometric properties of matter that are used in the various thermometers:

Note: You can visit UY1: Measurement Of Temperature for a in-depth review of the different types of thermometers.

A good thermometric property of matter should vary:

• continuously with temperature
• uniquely over the the range of temperature to be measured
• its variation should be measurable.

## Volume As Thermometric Property

Most solids or liquids or gases expand and contract their volume when the temperature around them changes.

Mercury is the only elemental metal that is liquid at ordinary temperatures. Mercury is silvery white and freezes into a soft solid like tin or lead at about -39 °C. Mercury does not wet glass or cling to it, and this property, coupled with its uniform volume expansion throughout its liquid range, makes it useful in liquid-in-glass thermometers.

Gases such as nitrogen or simply air are also suitable substances for use in volumetric gas thermometers. Typically, these gas thermometers work best at measuring very low temperatures.

Solid strips of different materials such as copper and aluminum can be made to stick together (bi-metallic strip). When the temperature of its surroundings changes, the different materials expand at different amounts, causing the bimetallic strip to bend, providing an indication to the change in temperature.

• Unable to give accurate readings.
• Assumption that all physical properties vary linearly with temperature is not always true. E.g. mercury and alcohol have different thermal expansion properties which cause them to display different readings in the same temperature.

Solution: Temperature scale independent of the physical properties of any substances $\rightarrow$  Thermodynamic scale (absolute temperature scale) $\rightarrow$ Gas thermometer (constant-volume thermometer)

Temperature readings are nearly independent of the type of the gas used when gas pressure is low and temperature is high.

Pressure of gas varies linearly with temperature.

Pressure extrapolates to zero when temperature is -273.15°C.(Absolute zero) $\rightarrow$ all particle motion cease (minimum internal energy).

##### Mini Physics

As the Administrator of Mini Physics, I possess a BSc. (Hons) in Physics. I am committed to ensuring the accuracy and quality of the content on this site. If you encounter any inaccuracies or have suggestions for enhancements, I encourage you to contact us. Your support and feedback are invaluable to us. If you appreciate the resources available on this site, kindly consider recommending Mini Physics to your friends. Together, we can foster a community passionate about Physics and continuous learning.

### 1 thought on “Thermometry & Thermometric Property”

1. How can I cite your website for a laboratory report?