05. Heat | Terms & Definitions | Science I | Class 10

  • Melting point of ice : The constant temperature, at which the ice converts into water is called the melting point of ice.
  • Latent heat of fusion : The heat energy absorbed at constant temperature during transformation of solid into liquid is called the latent heat of fusion.
  • Specific latent heat of fusion : The amount of heat energy absorbed at constant temperature by unit mass of a solid to convert into liquid phase is called the specific latent heat of fusion.
  • Boiling point of the liquid : During transformation from liquid phase to gas phase, heat energy is absorbed by the liquid, but its temperature does not change. The constant temperature at which the liquid transforms into gaseous state is called the boiling point of the liquid.
  • Latent heat of vapourization : The heat energy absorbed at constant temperature during transformation of liquid into gas is called the latent heat of vapourization.
  • Specific latent heat of vapourization : The amount of heat energy absorbed at constant temperature by unit mass of a liquid to convert into gaseous phase is called the specific latent heat of vapourization.
  • Regelation : The phenomenon in which the ice converts to liquid due to applied pressure and then re-converts to ice once the pressure is removed is called regelation.
  • Anomalous behaviour of water : In general, when a liquid is heated up to a certain temperature, it expands, and when cooled it contracts. Water, however, shows a special and exceptional behaviour. If we heat water from 0oC up to 4oC, it contracts instead of expanding. At 4oC its volume is minimum (due to contraction). If the water is heated further, it expands and its volume increases. The behaviour of water between its temperature from 0oC to 4oC is called anomalous behaviour of water.
  • Dew point temperature : Suppose unsaturated air at a certain temperature is taken and its temperature is decreased, a temperature is reached at which the air becomes saturated with vapour. This temperature is called the dew point temperature.
  • Absolute humidity : The vapour content in the air is measured using a physical quantity called absolute humidity. The mass of vapour present in a unit volume of air is called absolute humidity. Generally kg absolute humidity is measured in \frac{kg}{m^3}
  • Relative humidity : The ratio of actual mass of vapour content in the air for a given volume and temperature to that required to make the air saturated with vapour at that temperature is called the relative humidity.
  • Unit of heat : The units of heat are Joule (J) in SI units, cal (calorie) in cgs units. The amount of heat necessary to raise temperature of 1 g of water by 1oC from 14.5oC to 15.5oC is called one cal heat.
    • Similarly, the amount of heat necessary to raise the temperature of 1 kg of water by 1oC from 14.5oC to 15.5oC is called one kcal heat.
  • Specific heat : The amount of heat energy required to raise the temperature of a unit mass of an object by 1oC is called the specific heat of that object.
    • The specific heat capacity is denoted by letter c. The SI unit of specific heat is , J/kg oC and the CGS unit is cal/goC.
  • Principle of heat exchange : Heat I energy lost by the hot object = Heat energy gained by the cold object.


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