 Welcome back. After studying the basic principles of first law, now it is time for us to look at the zeroth law which will lead to the concept of temperature. We will soon see that first law by itself does not lead to enough quantitative information for us to solve exercises and problems in thermodynamics. So what we will do now is look at the immediate consequences of the first law. Then we will quickly look at another state postulates, let us call it state postulate 2. Then we will come to the need for a useful convenient property to handle some situations that we come across and naturally in thermodynamics a property is defined by a law. So we need a law, we call this the zeroth law. Remember that first law was our understanding of the way adiabatic partitions behave. Now we define another type of boundary known as a diathermic boundary which is essentially a non adiabatic boundary. And zeroth law is a characteristic of systems separated by diathermic boundary. So using this diathermic wall, so diathermic boundary we will state zeroth law. We will define that zeroth law will lead to definition of what we call isothermal states. Second part of zeroth law, the transitive property will lead to the idea of isotherms. We will look at how isotherms exist in state space and then we come to the concept of temperature. And finally we quickly look at how temperature is measured. The measurement of temperature is known as thermometry. Thank you.