Laws of Thermodynamics - SS1 Physics Lesson Note
The laws of thermodynamics are fundamental principles that govern the behaviour of energy and its interactions with matter. There are four laws of thermodynamics, but the first three are the most commonly discussed. Let's explore each law in detail:
1. First Law of Thermodynamics (Law of Energy Conservation):
The first law states that energy cannot be created or destroyed in an isolated system. It emphasises the principle of energy conservation, which means that the total energy of a closed system remains constant. The first law is often expressed using the equation:
ΔU = Q - W
where ΔU represents the change in internal energy of the system, Q represents the heat transferred into the system, and W represents the work done by the system.
In simple terms, the first law states that energy can be transferred between different forms (such as heat and work), but the total energy of a system remains constant.
2. Second Law of Thermodynamics:
The second law of thermodynamics introduces the concept of entropy and describes the direction of energy flow in a system. It has several statements, including:
- Heat flows naturally from hotter objects to colder objects. This statement implies that heat does not spontaneously flow from a colder object to a hotter object.
- The entropy of an isolated system tends to increase over time. Entropy is a measure of the system's disorder or randomness. The second law states that natural processes tend to increase the overall entropy of the universe.
- It is impossible to convert all heat into work in a cyclic process without any other effect. This statement refers to the efficiency limitations of heat engines.
The second law highlights the irreversibility of certain processes and provides insights into the efficiency of energy conversion.
3. Third Law of Thermodynamics:
The third law of thermodynamics states that as the temperature of a system approaches absolute zero (0 Kelvin or -273.15 degrees Celsius), the entropy of the system approaches a minimum or a constant value. This law establishes the reference point for measuring entropy and sets a limit on the achievable lowest temperatures.
The third law also states that it is impossible to reach absolute zero through a finite number of processes. However, it is important to note that achieving absolute zero is a theoretical concept that has not been achieved in practice.
4. Zeroth Law of Thermodynamics:
The Zeroth law states that if two systems are in thermal equilibrium with a third system, then they are also in thermal equilibrium with each other. It establishes the concept of temperature and provides the basis for temperature measurement and the definition of a temperature scale.
The laws of thermodynamics are foundational principles that underpin our understanding of energy, heat, and their interactions with matter. They have wide-ranging applications in various fields, including engineering, physics, chemistry, and environmental science.