Physics

# Expansion of Liquid and Gas

## Expansion of Liquid

• In case of liquid linear and superficial expansivities are absent.
• Liquid is heated in a vessel which expand itself so the expansion that we observe is called apparent expansion.
• Apparent expansion is always less than real or absolute expansion due to expansion of vessel.
1. Coefficient of apparent expansion or apparent expansivity ()
• The apparent change in volume per unit original volume per degree change in temperature is called apparent expansivity.
• or =
1. Coefficient of real expansion or real expansivity ()
• Real change in volume per unit original volume per degree change in temperature is called real expansivity. It is constant for a liquid.
• or =

Now,

Real expansion = Apparent expansion + Expansion of vessel.

or,

Where, =Cubical expansivity of vessel.

Note:

• A vessel completely filled by liquid is heated then volume of liquid overflow or on cooling volume of empty space above liquid is

=

• A liquid is placed in a vessel upon certain mark so that level of liquid remain at same mark at all temperature then,

• Liquid is placed in a vessel so that volume of empty space above liquid remain same at all temperature then,

=

## Change in density

• When temperature is increased, the volume of the constant mass also increase and hence the density decrease.
• .

## Dulong and Petit's Experiment

• When and be the height of liquid column in two sides of U shaped tube at and then,

Absolute expansivity () =

• The height - is measured with a cathetometer or a travelling microscope mounted vertically.
• This experiment is done to find the real expansivity of the liquid. ## Correction of Barometer

• When the height of barometer is observed at then true height is given by

, Where is linear expansivity of scale.

• The correct height is measured at , then reading at is observed then

## Anomalous Behavior of Water

• It is a different behavior of water where water expands on cooling from to and vice versa.
• Water has greatest density and least volume at
• Water freezes from top of pond, which is an example of Anomalous Behavior. Existence of aquatic life on ice age was possible due to this behavior too.
• Expansivity of water is -ve from to .
• Mean or average expansivity of water is 0 at . ## Expansion of Gas

Note:

For expansion of gas, study the topic "Gas Laws".