Name: Thermal Expansion of Liquid
Uploaded: 2019-07-19
Duration: 9 min 24 s
Description: Thermal expansion is the increase, or decrease, of the size of a body due to a temperature change. Thermal expansion is large for gases and small for liquids...

Question

What is difference between real and apparent expansion of a liquid? Establish the relationship between the co-efficients of those expansions. Discuss the effect of anomalous expansion of water on marine life.

Accepted Answer

When 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, 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.

Real expansion of liquid = Apparent expansion of liquid + Volume expansion of the container

Coefficient of real expansion of the liquid is defined as the ratio of real change in the volume to its original volume per $1 ° C$ rise in temperature. Its SI unit is ${" per °C " or " °C}^{- 1} " or " K^{- 1} " .$

Coefficient of apparent expansion of liquid is defined as the ratio of apparent change in volume of the liquid to its original volume per $1 ° C$ rise in temperature. Its SI unit is ${" per °C " or " °C}^{- 1} " or " K^{- 1} " .$

$γ_{r} = γ_{a} + γ_{g}$

A common observation seen in the behaviour of the substances is that they expand when heated as the density decreases and vice versa takes place when the material is cooled. This is how substances generally react to heat.

The general tendency of cold water remains unchanged until $4 ° C .$ The density of water gradually increases as you cool it. When you reach $4 ° C$ it’s density reaches a maximum. What water does next will astound you. When you cool it further to make some ice, i.e. $0 ° C$ , water expands with a further drop in temperature, meaning the density of water decreases when you cool it from $4 ° C$ to $0 ° C$ . The below graph explains this behaviour.

The effect of this expansion of water is that the coldest water is always present on the surface. Since water at $4 ° C$ is the heaviest, this water settles on the bottom of the water body and the lightest ie the coldest layer accumulates on the top layer. So in the winter, the top of the water is always the first to freeze over. Since ice and water both are a bad conductor of heat, this top layer of ice insulates the rest of the water body from the cold of the winter, thereby protecting all the life in the water body.

What is difference between real and apparent expansion of a liquid? Establish the relationship between the co-efficients of those expansions. Discuss the effect of anomalous expansion of water on marine life.

Important Questions on Thermal Expansion

Learn and Prepare for any exam you want !