SPECIFIC HEAT


"Amount
of heat energy required to raise the temperature of unit mass of a substance
by one Kelvin or 1° C is known as specific heat of the substance." 

MATHEMATICAL
EXPRESSION


If D Q is the amount of heat required to raise the temperature of "m" kg of the substance through ‘D T Kelvin , Then  
D
Q µ m .......(i)
D Q µ D T ........(ii) or D Q = m c D T 

where ‘C’ is the constant called specific heat of substance.  
OR


c = D
Q / m D T


UNIT
OF SPECIFIC HEAT


Unit of specific heat is J/kg K in S.I. system  
Experiments show
that specific heat of a particular material varies with temperature. Specific heat is not a precious concept for calculation because numbers of molecules per unit mass changes from material to material. 

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DETERMINATION
OF SPECIFIC HEAT


Specific heat of a solid substance can be determined by the "Method of Mixture" using the concept of the "law of Heat Exchange" i.e.  
heat lost by hot body = heat gained
by cold body


The method of mixture based on the fact that when a hot substance is mixed with a cold substance, the hot body loses heat and the cold body absorbs heat until thermal equilibrium is attained. At equilibrium, final temperature of mixture is measured. The specific heat of the substance is calculated with the help of the law of heat exchange.  
Let  
Mass of substance = m_{s} kg Mass of liquid = m_{l} kg Mass of calorie meter = m_{c} kg Initial temperature of the substance = T_{s} K Initial temperature of the liquid = T_{l} K Initial temperature of the calorie meter = T_{c} K Specific heat of substance = C_{s} = ? Specific heat of liquid = C_{l} Specific heat of the material of the calorie meter = C_{c} Final temperature of the mixture = T K 

According to the law of heat exchange  
Q_{LOST BY SUBSTANCE } = Q_{GAINED
BY LIQUID} + Q_{GAINED BY CALORIE METER}


M_{s }c_{s} (T_{s} – T) = m_{l }c_{l} (T – T_{l}) + m_{c} c_{c} (T – T_{c}) 

Which is the required value of specific heat of solid in J/ kg K.  