State change temperature is the temperature at which the substance changes from

# State change temperature is the temperature at which

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State change temperature is the temperature at which the substance changes from one state to another state. State change temperature are of following types: 1. Melting point It is the temperature (in °C or K) at which the substance changes from solid state to liquid state. 2. Boiling point
~ Page 26 of 79 ~ It is the temperature (in °C or K) at which the substance changes from liquid state to gaseous state. 3. Freezing point It is the temperature (in °C or K) at which a liquid changes from liquid to solid state. Theoretically it is equal to the melting point. However, practically some difference may observed . Coefficient of Thermal Expansion When a material is heated, it expends, due to which its dimensions change. Coefficient of thermal expansion, represents the expansion in material with increase of temperature. Thermal expansion coefficients are three types Coefficient of Linear Thermal Expansion The change in length of an object due change in temperature is r elated by “Coefficient of linear thermal expansion”. It denoted by “α L where, ‘l’ is the initial length of object, ‘Δl’ is the change in length, ‘Δt’ is the change in the temperature. Unit of α L is per °C. Coefficient of Area Thermal Expansion The change in area of an object due change in temperature is related by “Coefficient of Area thermal expansion”. It is denoted by “αA” where, ‘l’ is the initial length of object, ‘ΔA’ is the change in length, ‘Δt’ is the change in the temperature. Unit o f α A is per °C Coefficient of Volume Thermal Expansion The change in volume of an object due change in temperature is related by “Coefficient of volume thermal expansion”. It is denoted by “α V where, ‘l’ is the initial length of object, ‘ΔV’ is the change in length, ‘Δt’ is the change in the temperature. Unit of α V is per °C.
~ Page 27 of 79 ~ Specific Heat of Materials Specific heat of a material is defined as the amount of heat required to increase the temperature of unit mass of material by 1°C. It is denoted by ‘S’. where, ‘m’ is the mass of material in kg. ‘Q’ is the amount of heat given to material in Joule. ‘Δt’ is rise in temperature. Unit of specific heat in SI system is, Joule/kg °C. Latent Heat of Materials Latent Heat of a material is defined as the amount of heat required or released by change of the unit mass of material from one state to another state (Phase change). It is denoted by ‘L’. Latent heat is given by, Where, ‘Q’ is the amount of heat required / released by material (in joule), ‘m’ is the mass of material (in kg). Unit of Latent heat in SI system is Joule / kg. Fluidity of Materials It is a property of material which represents how easily a material can flow in liquid state. It is the reciprocal to viscosity of liquid material. Weldability of Materials It is the property of a material which presents how easily the two pieces of material can be welded together by applying pressure or heat or both.

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