 Let's solve a couple of questions on internal energy. So for the first one, we have a gas which undergoes the process as shown below. How does the internal energy of the gas vary in going from A to B? So gas goes from A to B. All right, pause the video and think about this. Okay, hopefully you gave this a shot. Now let's think about what is internal energy? So internal energy depends on temperature, right? So if the temperature increases, the internal energy increases. If the temperature decreases, so does the internal energy. And from ideal gas law, we know that temperature really is proportional to Pv, the product of pressure and volume. Now here, here at point A, let's say the pressure is PA and the volume is VA and at point B, the pressure is PB and the volume is VB. So the volume is increasing, it is going from VA to VB, but the pressure is decreasing. So we can't really say anything about the product of PV, the temperature at point A would be proportional to product of PNV, so PA multiplied by VA and temperature at B would be proportional to the product of PNV at this point, so PB multiplied by VB. But we don't know the values from the graph, so we can't say if this product is increasing or decreasing because one quantity is decreasing, that is pressure, but the other quantity is increasing and we don't know by how much. So we can't really say it may increase, decrease or even remain constant really. Just by the given information, we can't comment on how the internal energy is changing. Okay, let's look at one more question. Here we have the PV diagram for a monoatomic gas undergoing a thermodynamic process. Now this gas is going from point A to point B and we know the values of PA, PB, VA and VB. The question is to figure out the change in internal energy, delta U as the gas goes from A to B. Alright, pause the video and why don't you attempt this one on your own first. Okay, hopefully you gave this a shot. Now from the kinetic molecular theory of gas, we know that the kinetic energy of a monoatomic gas that is equal to 3 by 2, 3 by 2 PV, which is the same as the internal energy of a gas. So the internal energy of the gas at point A, we can write this as 3 by 2 PA into VA and the internal energy at point B, we can write that as 3 by 2 PB into VB. We already know the values of PA, VA, PB and VB. So let's put in these values and try to figure out the change in internal energy. We can take 3 by 2 as common and when we do put in the values of, so we start off by final minus initial. So PB into VB minus PA into VA. So PB is 8 into 10 to the power 3, VB is 1.2 and we are subtracting 1 into 10 to the power 3. So I'm just writing 10 to the power 3 into VA, which is 4.2. Okay, now when you work this out, this will come out to be equal to, and I encourage you to pause the video and work out this calculation. When you do work this out, you should get 8.1 into 10 to the power 3 joules. We need to just report 8.1 over here, so that's what it is. All right, you can try more questions from this exercise in the lesson and if you're watching on YouTube, do check out the exercise link which is added in the description.