Liquids do not have a definite shape. They take the shape of the container. Thus, we can specify a liquid by its volume. Hence, we can speak of volume expansion only for liquids. Expansion of liquids is much greater than that of solids.
A liquid is heated in a container. Heat flows through the container to the liquid. Which means that the container expands first, due to which the level of the liquid falls. When the liquid gets heated, it expands more and beyond its original level. We cannot observe the intermediate state. We can only observe the initial and the final levels. This observed expansion of the liquid is known as the apparent expansion of the liquid.
If we consider the expansion of the container also and measure the total expansion in volume of the liquid, then the expansion is termed as the absolute expansion of the liquid.
Expansion of container with liquid
In the figure L1 represents the original level at 
the level of the liquid first falls to L2, because the container gets heat first.
When the liquid gets heated, it expands much more than the container and its level rises to L3.
We can only observe the increase in level from L1 to L3. Intermediate level L2 goes unnoticed. The expansion we measure is the apparent expansion of the liquid. The corresponding coefficient is coefficient of apparent expansion.
The coefficient of apparent expansion is defined as the ratio of apparent increase in volume of the liquid to its original volume for every degree rise in temperature.
Coefficient of apparent expansion
If we evaluate the increase in volume of the liquid taking into account the expansion of the vessel also, then we say it is absolute expansion of the liquid. We can show that,
The coefficient of absolute expansion of a liquid = coefficient of apparent expansion + coefficient of cubical expansion of the material of the container.
| Liquid |
γ value at 20 °C |
| Water |
21x10-5/°C |
| Benzene |
122x10-5/°C |
| Mercury |
18x10-5/°C |
We may observe that liquids expand ten times more than solids.
