SSC CGL - Detailed Guide 2025
Self-Paced Course
Heat and Thermodynamics
Reference: Lucent GK, NCERT Class 6–12
1. Temperature and Heat
| Concept | Heat | Temperature |
|---|---|---|
| Definition | Form of energy transferred due to temperature difference | Degree of hotness or coldness of a body |
| Nature | Energy in transit | Measure of thermal condition |
| Quantity Type | Extensive (depends on mass) | Intensive (independent of mass) |
| Unit | Joule (J), Calorie (1 cal = 4.18 J) | Celsius (°C), Fahrenheit (°F), Kelvin (K) |
| Instrument | Calorimeter | Thermometer |
Heat always flows from high temperature to low temperature.
2. Modes of Heat Transfer
| Mode | Description | Example |
|---|---|---|
| Conduction | Heat transfer through solids without movement of particles | Heating a metal rod from one end |
| Convection | Heat transfer by actual movement of particles in fluids (liquids/gases) | Boiling water, sea breeze |
| Radiation | Heat transfer without any medium (through electromagnetic waves) | Sun's heat reaching Earth, infrared heating |
Conduction: solids only.
Convection: fluids only.
Radiation: all mediums including vacuum.
3. Thermometer Scales
| Scale | Freezing Point | Boiling Point | Absolute Zero | Relation |
|---|---|---|---|---|
| Celsius (°C) | 0°C | 100°C | –273.15°C | — |
| Kelvin (K) | 273 K | 373 K | 0 K | K = °C + 273 |
| Fahrenheit (°F) | 32°F | 212°F | –459.67°F | °F = (9/5)°C + 32 |
Kelvin is SI unit of temperature.
Absolute zero = 0 K (no molecular motion).
4. Laws of Thermodynamics
| Law | Statement | Key Implication |
|---|---|---|
| Zeroth Law | If A = B and B = C in thermal equilibrium, then A = C | Defines temperature as a measurable property |
| First Law | ΔQ = ΔU + W (Heat supplied = increase in internal energy + work done) | Conservation of energy in thermodynamic process |
| Second Law | Heat cannot flow from cold to hot body without external work | Explains direction of heat flow, introduces entropy |
| Third Law | As temperature approaches absolute zero, entropy of a perfect crystal → 0 | Entropy is minimum at 0 K |
Entropy = degree of disorder.
Heat engines (like Carnot engine) operate within limits of second law.
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