 Let us take up a numerical number. A sphere of aluminum 0.047 kg is placed for sufficient time in a boiling water, so that the sphere's temperature becomes 100 degree Celsius. So just write this one. A sphere of aluminum sphere of 0.047 kg is at 100 degree Celsius initially. It is immediately transferred to 0.14 kg copper calorimeter. So you have 0.14 kg of copper calorimeter inside which you are transferring this sphere. The calorimeter already has 0.25 kg of water, it already has 0.25 kg of water at 20 degree Celsius. The temperature of the water rises and the final temperature becomes 23 degree Celsius. You need to find out specific heat of aluminum, how much it is. Specific heat of aluminum is what? What is given is specific heat of copper which is 0.386 into 10 square 3 joules per degree Celsius. What is specific heat of water? How much it is? Remember 4.18 or 4.2 whatever. 4.18 into 10 square 3 joule per kg per degree Celsius. Who is losing heat? Aluminium and who is gaining? Copper. Copper and water. Just substitute the values over there. What is the heat lost by the aluminum? M which is 0.047 into specific heat of aluminum into delta D is what? For aluminum. 100 to 23 it drops. So 77, this into 77. This is the heat lost by the aluminum. This should be equal to heat gained by the copper. How much? Mass of copper is 0.14. Specific heat of copper and 386 10 is power 3 into delta T of copper is what? 3. From 20 it goes to 23. 3.24. Now water is also into 4.18 into 10 is power 3 into 3. You are telling this only? All of you? How much you are telling? You have the answers. Tell me. No, approximately also it is. So when you solve it properly, you will get specific heat of aluminum to be equal to 911 joule per kg. Calculation. But you should know which side you have approximated. Whether you have approximated to get less than the actual answer or more than the actual answer. Are you getting it? What I am trying to say? Approximation is fine. But you should know which side you are in. Try to correct your calculations. You have to do it again. You have to do it right the first time. If you make a mistake, it becomes very difficult to identify it. I will quickly discuss the next property as in I will just introduce it. I will not get into too much of details of it because time is not permitting. The next property that we are going to take up is change of states. So you have suppose we have three states solid although there are actually two or three more states but we are not getting into all that. We are talking about the usual three states. Three states of matter. So solid can become liquid if you provide heat. This process is called what? What is this process? This is called melting. Technically this is also called fusion. Then vaporization. This heat. This is heat required to fuse the solid. This is the heat required to vaporize. So let us say this is delta QF. This is delta QV less. Now when vapor becomes liquid, this is what absorption of heat. This much heat will be absorbed but when vapor is becoming liquid, same amount of heat will be released. Getting it? And similarly when liquid is becoming solid, delta QF will be released. And also there is process where solid directly becomes vapor that is sublimation but we are not getting into all that. These are the process when vapor becomes liquid. This process is called what? Condensation. When liquid is becoming solid, this is solidification. Now one unique thing about the transition is that when transition happens temperature is constant. What is temperature? A measure of the binding energy of the molecules. So when you get the heat and the state change is happening, binding energy does not change. Then what is changing? Potential energy. Potential energy. And what is potential energy? Energy purges because of the position. So the molecules are going further away from each other. So the potential energy is increasing. So whatever heat you are giving it, it is increasing the potential energy. The binding energy is not increasing in the state change. Getting it? So it is a constant temperature process during the transition. And in case of water and in case the pressure is 1 atmosphere, this transition happens at 0 degree Celsius and that transition happens at 100 degree Celsius. So transition temperature depends on the pressure as well as what is the material. But temperature will remain constant at a particular pressure. Any doubts? No? So the heat that is required to melt this solid completely should depend on what? Should depend on how much is the solid? How much? How many kgs? Right? And should it depend on nature? That is it. Temperature is anyway not changing. Are you getting it? So when it is melting, when it is melting, delta Q is just mass into a constant which is latent heat of fusion. Same formula holds good when liquid is becoming solid. Solidification also. But this time when liquid becomes solid, it will release the same amount of air. Are you getting it? Now one unique thing here, this is what? What is this? Mass of what? This is not a total mass. This is the mass which has changed the state. Out of 5 kgis, you just melted 1 kg. So this is 1 kg only. When you write delta Q is equal to Ms delta T. You are taking entire mass. But when you are writing M into Lf, you are taking only that mass which is changing the state. Remember that. This is melting or solidification both. And this is a huge amount of energy. Latent heat of fusion is usually a very big number. And you see that, let me first introduce vaporization also. For vaporization or condensation, the amount of heat is mass of this liquid that is vaporizing into latent heat of vaporization. Now have you ever seen like how your mom used to make sure that milk is the hot milk very quickly. How it happens? What she does? You put it below the fan. Have you ever seen that? So when you put it below the fan and fan is rotating, a lot of vaporization happens. The vapor comes out from the milk. Now during the vaporizing, it needs that much heat. So from where it will take the heat? From the remaining milk, whatever is vaporizing, it will take the heat from the remaining milk and go away and vaporize. So the remaining milk is getting cooled down faster and faster because vaporizing is happening. Same thing happens when the sweat and wind is blowing. Then our sweat is vaporizing. When sweat is vaporizing, the heat which is required for it to vaporize, it will take from our body. So we feel cold. That is the whole reason why humans sweat when there is a hot conditions. So that you feel cold because vaporization should happen from this heat. So next class we will take it more quantitatively and we will solve a lot of numerical on it. We try to finish this challenge. Okay, any doubts? Nothing?