Learning Objectives · Part 3

heat energy required to rise the temperature of gram of water through °C. Kilocalorie: One kilocalorie is defined as the amount of heat energy required to rise the temperature of kilogram of water through °C. . EFFECT OF HEAT ENERGY When a certain amount of heat energy is given to a substance, it will undergo one or more of the following changes: Temperature of the substance rises. The substance may change its state from solid to liquid or from liquid to gas. The substance will expand when heated. The rise in temperature is in proportion to the amount of heat energy supplied. It also depends on the nature and mass of the substance. About the rise in temperature and the change of state, you have studied in previous classes. In the following section, we shall discuss about the expansion of substances due to heat. . . Expansion of Substances When heat energy is supplied to a body, there can be an increase in the dimension of the object. This change in the dimension due to rise in temperature is called thermal expansion of the object. The expansion of liquids (e.g. mercury) can be seen when a thermometer is placed in warm water. All forms of matter (solid, liquid and gas) undergo expansion on heating. a) Expansion in solids When a solid is heated, the atoms gain energy and vibrate more vigorously. This results in the expansion of the solid. For a given change in temperature, the extent of expansion is smaller in solids than in liquids and gases. This is due to the rigid nature of solids. The different types of expansion of solid are listed and explained below: . Linear expansion . Superficial expansion . Cubical expansion . Linear expansion: When a body is heated or cooled, the length of the body changes due to change in its temperature. Then the expansion is said to be linear or longitudinal expansion . The ratio of increase in length of the body per degree rise in temperature to its unit length is called as the coefficient of linear expansion .