Thermodynamics
Physics · ऊष्मागतिकी
📋Quick Overview
Thermodynamics is the branch of physics that deals with heat and its relationship with work and energy. 'Thermo' = heat, 'Dynamics' = motion/change. It has 4 laws (0th, 1st, 2nd, 3rd) that govern how heat energy works in the universe. These laws explain why engines work, why your fridge cools food, and why perpetual motion machines are impossible!
📖Four Laws of Thermodynamics
| Law | Statement (Simple) | Key Concept | Daily Life Example |
|---|---|---|---|
| Zeroth Law | If A is in thermal equilibrium with B, and B with C, then A is also in equilibrium with C | Defines temperature — basis of thermometers | Thermometer works on this: it reaches same temp as your body |
| First Law | Energy can neither be created nor destroyed, only converted (ΔU = Q - W) | Conservation of Energy applied to heat | Car engine: fuel's chemical energy → heat → mechanical work |
| Second Law | Heat cannot flow from cold body to hot body on its own (without external work) | Entropy always increases; defines direction of heat flow | Fridge needs electricity to move heat from cold inside to warm outside |
| Third Law | It is impossible to reach absolute zero (0 K) in a finite number of steps | Absolute zero can never be achieved perfectly | We can get very close to 0 K but never exactly reach it |
📝Heat Engine, Refrigerator & Entropy
- •Heat Engine: Converts heat into work. Takes heat from HOT source, does work, and rejects remaining heat to COLD sink. Example: Car engine, steam engine
- •Efficiency of heat engine is ALWAYS less than 100% (some heat is always wasted). Carnot engine gives maximum possible efficiency.
- •Refrigerator: Works OPPOSITE to heat engine. Takes heat from cold inside and throws it to warm outside. Needs external work (electricity).
- •Entropy = measure of disorder/randomness. 2nd Law says entropy of universe always INCREASES. Things naturally go from order to disorder.
- •Perpetual Motion Machine (PMM) is IMPOSSIBLE: 1st Law says you can't create energy from nothing (PMM Type 1). 2nd Law says you can't convert 100% heat to work (PMM Type 2).