JEE MAIN ADVANCE 11th PCM Physics Heat & Thermodynamics

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Hello, students, in this module we are going to look at a few important terms related to Calorimetry and the very important principle of Calorimetry based on which we have a number of questions coming up in the further modules. So, I want you to pay very, very close attention to this particular module because the concepts that we learn out here is going to be directly applied in the numericals.

So, to begin with, the important terms with Calorimetry. The first term that I will be encountering is Thermal Capacity. Now, what exactly is the Thermal Capacity? Now Thermal Capacity is defined as amount of heat required in order to raise the temperature of the entire body by 1 degree centigrade. Whereas now, if I have to compare this with specific heat capacity, it is the amount of heat required to raise the temperature of unit mass of a substance by 1 degree. So, the difference between thermal capacity and specific heat capacity comes in the fact that it is for the entire body and this is for a unit mass. So, if I have the relation here which will give me delta Q is equal to mC delta T, hence it can also be written as what, H into delta T. So, if I cancel delta T from both sides of the equation, I get my thermal capacity as the product of mass into specific heat capacity. So, this is a very important relation to be remembered, my dear students. The unit of thermal capacity is nothing but Joules per degree centigrade or Joules per Kelvin.

Now, in this list the next important term that we have is the water equivalent. Dear students, let me tell you water equivalent generally appears in the numerical and I don’t want anyone of you to get confused because when we have a mixture present in a calorimeter, they don’t mention to us about the mass of the calorimeter or its specific heat capacity. They give us directly what is the water equivalent of the calorimeter. So, from there you should not be confused, you should be able to use the concept of water equivalent very nicely to find out what will be the raise in the temperature of the calorimeter. So, here we try to understand, what exactly is meant by calorimeter? Let’s say, we have a block whose mass is m and its specific heat capacity is C and the change in temperature is delta T. So, how much heat will be related to this particular block. Delta Q is equal to mC delta T. Now let’s say the same amount of heat I use to raise the temperature of water by an equal difference. So, the same amount of heat for raising the temperature of water by equal level then how much water should I be taking that is known as the water equivalent. So, I can write down this delta Q is nothing but equals to W into 1 into delta T where the delta T will get cancelled from both sides of the equation. Hence, I will get the value of my value equivalent is equal to nothing but product of mass into specific heat capacity.

Having done this, let’s just go ahead with this to look at the basic principles of Calorimetry. What does it say? Let’s say we have a block which has got a mass m1, specific heat capacity C1. It is at a temperature T1 degree centigrade. We have got another block, whose mass is m2, its specific heat capacity is C2 and it is ata temperature T2. Now, given is temperature T1 is greater than T2. So, heat is going to flow from the body at a higher temperature at the body at a lower temperature and this is the direction of the heat flow. Now, after some time there is going to be a state of thermal equilibrium where the temperature of both the bodies is going to be equal. So the principle of Calorimetry states that heat lost by a body at higher temperature is equal to the heat gained by the body at a lower temperature. So, having done that, what is the amount of heat lost by the body at a higher temperature? It is m1C1 into T1 minus T that is the temperature difference for the body at a higher temperature. And what is the heat gained by a body at the lower temperature? It is m2C2 into T minus T2. Now, equating them this is what is the most important principle that we are learning in this particular module. Now, having done that, T is the temperature of equilibrium and if we solve it, we get the temperature of equilibrium as m1C1T1 plus m2C2T2 divided by m1C1 plus m2C2.

So having done these, students, we will be using the same concept in the numericals ahead.

Thank you very much.

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