Laws of Thermodynamics (First and Second Laws) - SS1 Physics Lesson Note
The laws of thermodynamics are fundamental principles that govern the behaviour of energy and its transfer in physical systems. There are four laws of thermodynamics, but the first and second laws are particularly significant. Here's a brief explanation of these two laws:
1. First Law of Thermodynamics (Law of Energy Conservation):
The first law of thermodynamics states that energy cannot be created or destroyed in an isolated system. It can only change its form or be transferred from one system to another or between different parts of the same system. The total energy of an isolated system remains constant, and any energy added to the system is equal to the sum of the work done on the system and the heat added to the system. Mathematically, it is expressed as:
ΔU = Q - W
where ΔU is the change in internal energy of the system, Q is the heat added to the system, and W is the work done by the system.
This law is often referred to as the law of energy conservation since it states that the total energy of a closed system remains constant, and energy can be converted from one form to another.
2. Second Law of Thermodynamics:
The second law of thermodynamics introduces the concept of entropy, which is a measure of the disorder or randomness of a system. It states that in any natural or spontaneous process, the total entropy of an isolated system always increases or remains constant but never decreases. In other words, natural processes tend to move towards a state of higher disorder or randomness.
The second law of thermodynamics can be stated in various forms, including:
- Heat flows spontaneously from a hot object to a cold object and never the reverse (Clausius statement).
- It is impossible to construct a device that operates in a cycle and extracts heat from a single reservoir to perform an equivalent amount of work (Kelvin-Planck statement).
This law has profound implications, such as the irreversibility of certain processes, the limitations on the efficiency of heat engines, and the concept of entropy as a measure of the availability of energy.
These two laws of thermodynamics provide fundamental principles for understanding and analysing energy systems, heat transfer, and the behaviour of physical processes. They have wide-ranging applications in various fields, including engineering, physics, chemistry, and environmental science.