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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 =


Real expansion = Apparent expansion + Expansion of vessel.


Where, =Cubical expansivity of vessel.


  • 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


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