SPECIFIC HEAT CAPACITY AND HEAT CAPACITY

 

Specific heat capacity 

 Specific heat capacity can be defined as it is the amount of heat energy required to raise the temperature of unit mass of a substance through one degree Centigrade. 

 Different bodies have different values of their specific heat depending upon their nature. Some of the examples are given below

 How we can derive formula for specific heat?

 Based on a simple activity we can derive a formula for specific heat. 

Take two beakers and name them as A and B. Fill the two beakers with some water. Let us assume that the mass of water in both the beakers be 1 kg. 

 And the water present in both the beakers is at room temperature. 

 Let us assume that we have to raise the temperature of water in beaker A to 50⁰ centigrade. And we have to raise the water in beaker B to 70⁰ Centigrade for a given constant time.

 In order to do so definitely we have to supply more heat energy to beaker B as change in temperature for beaker B is more than that of beaker A. 

 So we can conclude that. 

 Heat energy required is directly proportional to the change in temperature. 

  

Here “Q” represents heat and “t” represents temperature.

We repeat the same activity for the second time 

But in this case we take different masses. And the same change in temperature. 

So let us assume that water in beaker B is 1 kg and mass of water in beaker A is 2 kg. And let us assume that the temperature of water in both the beakers has to be raised to 50⁰ centigrade each for a given constant time.

So in this case definitely more heat energy should be supplied to beaker B, as it has more mass when compared to water in Beaker A. Even though change in temperature is same. 

So heat energy required is directly proportional to mass of the body to change its temperature. 

From the above two proportions, we have   

To convert proportion to an equation we multiply with a constant say “S”

Therefore we get 

 From the above equation, we can also write 

 This is the required formula for specific heat.

CGS unit of specific heat is cal / g ⁰c

SI unit of specific heat is J / kg-k   (DIMENTIONAL FORMULA IS M⁰ L² T^-2 K^-1 )

• Where  M = Mass
• K = Temperature
• L = Length
• T = Time

The specific heat value varies from body to body depending upon its nature. 

 The substance which has higher specific heat value has more thermal inertia.

i.e, these materials has more ability to restrict the sudden changes in their temperatures.

They neither get heated up faster nor cooled down faster.

 But the materials having low specific heat value can get heated up faster and can be cooled down faster because of less thermal inertia.

 Daily life applications of specific heat

 We have a lot of examples where we can observe the concept of specific heat in our daily life. The best example is sea breeze and land breeze.

1)    During daytime when sun raises up, Land gets heated up fast when compared to seawater, as water has a high specific heat value. 

 So as a result water remains cool even though land becomes hot. 

 So air present on the land will be warm(less density) when compared to the air present on the water (much density). So it forms high pressure area on sea water and low pressure area on land due to difference in the densities.

 As a result The Gentle Wind blows from sea to the land. This is what we are calling as sea breeze. 

 And at the time of sunset the land gets cold faster when compared to the seawater. 

 So it forms high pressure area on the land and low pressure area on the seawater. 

 As a result a Gentle Wind blows from land to water. This is what we are calling as land breeze. 

2)  We can take watermelon as a best example to understand the concept of specific heat. 

When a watermelon kept in a Refrigerator is taken out, we can observe the difference in the coolness of the outer peel of the watermelon and the pulp inside the watermelon because of difference in their specific heat values 

As the pulp of watermelon contains 90% of water, it has more specific heat when compared to the outer surface. 

3) Also we use water as coolant to cool down the heated up engines of vehicles.

Like this we can observe number of examples of specific heat in our daily life where we make use of this concept but actually without knowing the reason.

Heat capacity or thermal capacity 

 

Heat capacity can be defined as it is the amount of heat energy required to raise the temperature of entire mass of a substance by 1 degree centigrade. 

 it is denoted with a symbol “H”.

  And the formula is

 

 CGS unit of thermal capacity is cal/⁰c

SI unit of thermal capacity is J/K

DIMENSIONAL FORMULA IS   M L²T⁻² K⁻¹ 

 

 Relation between the specific heat capacity and thermal capacity 

 We know,  S=Q/m∆t  and  H=Q/∆t

 From the above two equations we have