Thermal expansion

 

Thermal expansion :

The increase in size on heating is called thermal expansion.

Solid can expand in three different ways.

1.     Linear expansion.

2.     Aerial expansion  or  superficial expansion.

3.     Volume expansion  or cubical expansion.

But in liquid and gasses volume expansion take place.

Reason :

Why solid expand on heating?

Molecule of solid are tightly packed together so ,when solid is heated the amplitude of molecule increases and hence over all size of solid increases.

Linear expansion :

The increase in length on heating of solid is called is called linear expansion.

                   

                     

 

It has found experimentally that the change in length "`\triangle L`"is directly proportional to the original length and to the change in temperature.

`\triangle L\propto L\;`

`\triangle L\propto\triangle T`

By combining eq 1 and 2:

`\triangle L\propto L\triangle T`

`\triangle L=\alpha L\triangle T`

`\alpha=\frac{\triangle L}{L\triangle T}`

Where  `\alpha` (alpha) is called coefficient of linear expansion and its value depends upon the material of a substance.

 

`\alpha` (alpha):

                It is defined as the change in length per unit original length per unit change in temperature

Volumetric expansion :

The  increase in volume on heating of solid is called volumetric expansion .

It has found experimentally that the change in volume `\triangle v` is directly propotional to the original volume and to change in temperature .

`\triangle v\propto v\;`

`\triangle v\propto\triangle T`

By combining eq 1 and 2:

`\triangle v\propto v\triangle T`

`\triangle v=\beta v\triangle T`

`\beta=\frac{\triangle v}{v\triangle T}`

 Where  `\beta` (Beta) is called coefficient of volumetric expansion and its value depends upon the material of a substance.