What Makes a Process Reversible or Irreversible?
Reversibility, the realm of thermodynamics, refers to the characteristic in regards to a particular process that can be reversed. Most importantly, the system should be restored to its primary state without leaving any effect on the other systems which were involved. In simpler terms, the meaning of irreversible is a process that can be reversed without leaving any trace on the surroundings. Irreversible in the process can be owed to the interaction of that system with other processes. An ideal example of this process would be the singular swing of a frictionless pendulum.
What is Reversibility Meaning as Per Scientific Terms?
In scientific terms, the reversibility meaning is determined to be the net heat and work exchange between the system and surroundings (for original + reverse process) is zero. These processes take the least amount of work in the realm of work consuming devices. In proportion, they give the maximum output, owing to which they produce ample interest as they function in an optimum manner. They also act as a highlight to reflect upon the theoretical limits to corresponding irreversible processes. Reversible processes also reflect upon the definition of the second law efficiency for actual processes, which is related to the degree of approximation in regards to the corresponding reversible processes.
In practical terms, it would take an infinity for the whole reversible process to complete itself, thus owing to this contingency, perfectly reversible processes are impossible. However, there is a practical solution to it, which provides us with the same result. So if the system which is going through the changes reacts much faster compared to the change which is being applied to it, in such a rare case, the change caused due to reversibility would be negligible, in other words, not noticeable.
[Image will be Uploaded Soon]
Example of Reversibility
In an optimum reversible process, the energy exerted from the said work being done by the system would be optimum. In other words, to understand the example of reversibility, it would be maximized. The heat being exerted the said performance of the process would be nil to reach this maximum output. But replicating the same in reality is not physically possible, as heat exerted from the performance of the said process cannot be fully converted into work, and some of the heat will always be lost.
This heat will be generally lost to the things surrounding the process. But there are some cases in which the theoretical basis of this proposition does stand true. For instance, in the process of isothermal expansion of an ideal gaseous particle in a piston-cylinder arrangement, this does stand true as no heat whatsoever is lost in the process. In scientific terms, the net change in the composite entropy of the whole system and the surroundings revolving around the process will be zero.
The usage of this process is mainly evident in the creation of heat engines for large commuting vehicles like chartered flight and freight trains. Since it helps minimise the heat lost from the process, it aids the designers in manufacturing the requisite engines, giving the maximum output by reducing the heat exerted from the process. For instance, if an engine gives out less heat, then in one cycle, the energy put into the process will be put to use for the functioning of the vehicle, and less energy will be wasted in the form of heat. The main source through which heat is lost friction is that a certain amount of friction is inevitable as in any process. Thus even in the ideal example, the product used for charging the whole arrangement was gaseous in nature, as negligible to no heat is lost in processes surrounding gaseous particles.
Nicholas Tesla was one of the first pioneers who actually applied this in their work. The Tesla Turbine invented by him had disks that revolved for fastening the said machine to its respective shaft, which was in turn operated by an engine. If the whole process was reversed, meaning, if the turbine’s operation was reversed, the same disks acted as a pump. Another common day example of a reversible process can be seen in the functioning of a reservoir. Heat transfer between a reservoir and a system is an externally reversible process if the outer surface of the system is at the temperature of the reservoir.
[Image will be Uploaded Soon]
FAQs on Reversibility in Physics: Concepts, Examples & Significance
1. What is a reversible process in simple terms?
A reversible process is a theoretical process that can be reversed to return both the system and its surroundings to their exact original states without any change. Imagine a slow, frictionless piston compressing a gas. If you reverse the action just as slowly, the gas expands back to its initial volume and pressure, and no energy is lost as heat. It's an ideal process that happens so slowly that the system is always in equilibrium.
2. What is the main difference between a reversible and an irreversible process?
The main difference lies in whether a process can be perfectly undone. Here's a simple breakdown:
- A reversible process is an ideal process that can be reversed to restore the initial state of both the system and surroundings. It occurs infinitely slowly with no energy loss due to friction or heat.
- An irreversible process is any real-world process that cannot be perfectly reversed. Factors like friction, heat loss, or rapid changes cause a permanent change (usually an increase in entropy) in the surroundings. All natural processes are irreversible.
3. Why are perfectly reversible processes not possible in the real world?
Perfectly reversible processes are not possible because real-world systems always have factors that cause energy loss. These factors, known as dissipative effects, include friction, heat transfer between bodies with a temperature difference, and rapid changes that are not in equilibrium. Because of these effects, you can never get back 100% of the initial energy to perfectly restore both the system and its surroundings.
4. What are some examples of processes that are considered almost reversible?
While no real process is perfectly reversible, some can be approximated as reversible if they happen very slowly and with minimal friction. Examples include:
- The slow, frictionless compression or expansion of a gas in a cylinder.
- A gradual phase change, like ice melting into water at a constant temperature of 0°C.
- The slow transfer of a small amount of heat between two bodies that are at nearly the same temperature.
These are idealisations used in physics to simplify calculations and understand theoretical limits.
5. What conditions are necessary for a process to be considered reversible?
For a process to be theoretically reversible, two main conditions must be met. First, the process must be quasi-static, meaning it happens so slowly that the system is always in thermodynamic equilibrium at every single stage. Second, the process must be non-dissipative, which means there are no energy-wasting effects like friction, electrical resistance, or viscosity. Fulfilling both of these conditions perfectly is practically impossible.
6. If reversible processes don't actually exist, why is the concept of reversibility so important in physics?
The concept of reversibility is crucial even though it's an ideal. It serves as a theoretical benchmark or a standard of maximum efficiency. By comparing a real (irreversible) process to its ideal reversible counterpart, engineers and scientists can measure the efficiency of engines, refrigerators, and other thermodynamic systems. It helps us understand the theoretical limits of what is possible and quantify the energy lost in real-world applications.
