In Thermodynamics (Class 11 Physics and Chemistry), understanding how a system changes state is crucial. Processes are broadly classified into two types: Reversible and Irreversible.
All natural and spontaneous processes in the universe are Irreversible. The concept of a Reversible process is used purely as a theoretical maximum limit to calculate the maximum efficiency of engines (like the Carnot Engine).
A Reversible Process is an ideal, hypothetical process that occurs infinitely slowly, in such a way that the system and its surroundings can be exactly restored to their initial states by reversing the direction of the process.
An Irreversible Process is a real-world process that cannot be completely reversed. Once it happens, the system and surroundings cannot both be restored to their exact original states without external work.
| Feature | Reversible Process | Irreversible Process |
|---|---|---|
| Speed | Infinitely slow | Fast / Finite speed |
| Equilibrium | System is always in equilibrium | Equilibrium only at initial and final states |
| Energy Loss | No loss of energy (ideal) | Energy is lost (friction/heat dissipation) |
| Reality | Theoretical / Ideal | Real / Natural |
In physics, melting ice is often treated as reversible *if* it is done infinitely slowly at exactly 0°C. However, in practical daily life, melting an ice cube on a table is an irreversible thermodynamic process.
SI Unit of Electric Current
The SI unit of electric current is Ampere (A), named after André-Marie Ampère. 1 Ampere = 1 Coulomb per second. Ohm's law and current formula explained.
SI Unit of Length
The SI unit of length is the metre (m). Defined as the distance light travels in vacuum in 1/299,792,458 seconds. Learn prefixes: km, cm, mm, nm, Å.
SI Unit of Pressure
The SI unit of pressure is the Pascal (Pa). 1 Pa = 1 N/m². Atmospheric pressure = 101,325 Pa. Learn formula, dimensional formula, and unit conversions.
SI Unit of Resistance, Resistivity, and Capacitance
Learn the SI units of electrical resistance (Ohm), resistivity (Ohm-meter), and capacitance (Farad). Understand their definitions and formulas.
SI Unit of Resistivity — Ohm-Metre (Ω·m)
The SI unit of resistivity is ohm-metre (Ω·m). Derived from ρ = RA/L. Definition, formula, dimension, and resistivity values of common materials explained.
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