Thermal Expansion Of Solids

Thermal expansion is the basic principle that a thermometer works on. The mercury in the reservoir in the bottom of the thermometer is immersed in a hot or cold object. On doing so, the mercury in the thermometer contracts and expands changing the level indicated on the thermometer. The thermometers are always calibrated and after a few minutes, the level of mercury inside becomes stable and unchanging. This new level with the calibrated thermometer tells us the temperature of the object we are measuring. The same principle of thermal expansion applies to gases as well. The constant volume gas thermometer is an example of the application of thermal expansion in gases.,/p>

Thermal Expansion in Metals

Thermal expansion applies to other metals too. After all mercury is also a metal. It is a well-known phenomenon now that substances expand on heating and contract on cooling. If you heat a body, it alters its dimensions.

Depending on the shape of the body, the expansion can occur in length in which case it is called Linear Expansion. If we take a square tile and heat it, the expansion will be on two fronts, length and breadth, here it is called Area Expansion. If we take a cube and heat it, all its sides expand and now the body experiences an increase in the overall volume due to this and it is called Volume Expansion. The formula used to represent the thermal expansion in a body is;

$\frac{\Delta l}{l} = \alpha _{1}.\Delta T$

Here, the alpha represents the coefficient of linear expansion and it is a characteristic of the substance the body is made of. For example, for the same temperature rise, copper expands almost five times more than glass. Generally, metals expand more and have higher values of alpha compared to gases and liquids.

Volumetric Expansion Coefficient

It is important that we consider the volumetric thermal expansion of substances since most of the things we use in real life are three dimensional and thereby undergo three-dimensional expansion ie volumetric expansion. The formula to represent the volumetric thermal expansion is;

$\alpha _{v} = \frac{\Delta V}{V}.\frac{1}{\Delta T}$

In this article, you learnt about the thermal expansion of metals and their reactions to heat in general. In the next article, you will find an explanation about the Anomalous expansion of water, the phenomenon that prevents all the water in the world from freezing over. To learn more, please subscribe to BYJU’s and fall in love with learning.

Practise This Question

A steel scale measuresthe length of a copper wire as 80.0 cm when both are at 20C (the calibration temperature for scale). What would be the scale read for the length of the wire when both are at 40C ?  (Given αsteel=11×106 per0 C and αcopper=17×106 per 0C)