Newton’s Law of Cooling

Sir Issac Newton tell about cooling any system in 1701.

According to this law the rate of change in the temperature is proportional to the difference between the temperature of the object and the temperature of surrounding environment.




The Four Laws of Thermodynamics

1. The Zeroth Law

If two bodies are in thermal equilibrium with other third body then they are also in thermal equilibrium with each other, this is called the zeroth law.

Assume that there are two system A and B which are in thermal equilibrium with other third system C. Then A and B also will be in thermal equilibrium.




2. The First Law

According to the first law of thermodynamics, the energy always conserved in isolated system. Energy cannot be destroyed or cannot be created. It can changes in other forms but it always conserve. This law also called The Principle of Conservation.

If Q is given heat to system by surroundings then some part of it change in internal energy (U) and some part change in work done by system (W). So total energy always conserve.




3. The Second Law

According to the second law of thermodynamics, heat always transfer to low temperature from high temperature. Heat cannot transferred to high temperature from low temperature without any extra energy. In other words, there is not any kind of engine possible that convert whole energy into work.

There are two statements given which based on this second law:

  1. Kelvin-Plank Statement
  2. Clausius Statement




4. The Third Law

According to this law, at 0k temperature, all pure crystalline solids have minimum entropy (0). Entropy cannot be in negative. It always in positive and it increases regularly in the universe.