Thermal Physics
Temperature, gas behaviour, the laws of thermodynamics, and heat transfer mechanisms.
A. Temperature Scales
Scale Comparison
| Scale | Freezing Point | Boiling Point | Conversion |
|---|---|---|---|
| Celsius (°C) | 0 °C | 100 °C | °C = K − 273 |
| Kelvin (K) | 273 K | 373 K | K = °C + 273 |
| Fahrenheit (°F) | 32 °F | 212 °F | °F = (9/5 × °C) + 32 |
Celsius (°C)
Freezing Point0 °C
Boiling Point100 °C
Conversion°C = K − 273
Kelvin (K)
Freezing Point273 K
Boiling Point373 K
ConversionK = °C + 273
Fahrenheit (°F)
Freezing Point32 °F
Boiling Point212 °F
Conversion°F = (9/5 × °C) + 32
Key Conversions
K = °C + 273
°C = K − 273
Absolute zero = 0 K = −273°C (minimum possible temperature) · Kelvin is the SI unit
B. Gas Laws
All Gas Laws
| Law | Variables | Statement | Formula |
|---|---|---|---|
| Boyle's Law | P & V (constant T) | Pressure and volume are inversely proportional | P₁V₁ = P₂V₂ |
| Charles's Law | V & T (constant P) | Volume and temperature are directly proportional | V₁/T₁ = V₂/T₂ |
| Gay-Lussac's Law | P & T (constant V) | Pressure and temperature are directly proportional | P₁/T₁ = P₂/T₂ |
| Avogadro's Law | V & n (constant T, P) | Equal volumes of gases at same T and P contain equal molecules | V₁/n₁ = V₂/n₂ |
| Ideal Gas Law | All variables | Combines all gas laws | PV = nRT |
Boyle's Law
VariablesP & V (constant T)
StatementPressure and volume are inversely proportional
FormulaP₁V₁ = P₂V₂
Charles's Law
VariablesV & T (constant P)
StatementVolume and temperature are directly proportional
FormulaV₁/T₁ = V₂/T₂
Gay-Lussac's Law
VariablesP & T (constant V)
StatementPressure and temperature are directly proportional
FormulaP₁/T₁ = P₂/T₂
Avogadro's Law
VariablesV & n (constant T, P)
StatementEqual volumes of gases at same T and P contain equal molecules
FormulaV₁/n₁ = V₂/n₂
Ideal Gas Law
VariablesAll variables
StatementCombines all gas laws
FormulaPV = nRT
Key Gas Law Formulas
Boyle's Law
P₁V₁ = P₂V₂
Temperature constant — pressure × volume = constant
Charles's Law
V₁/T₁ = V₂/T₂
Pressure constant — volume ÷ temperature = constant (T in Kelvin!)
Ideal Gas Law
PV = nRT
R = 8.314 J/mol·K (Universal Gas Constant) · T must be in Kelvin
C. Thermodynamics
Laws of Thermodynamics
| Law | Statement |
|---|---|
| Zeroth Law | If A is in thermal equilibrium with B, and B with C, then A is in equilibrium with C — the basis of temperature measurement |
| First Law | Energy is conserved: ΔU = Q − W (change in internal energy = heat added − work done by system) |
| Second Law | Heat flows spontaneously from hot to cold; entropy of an isolated system always increases |
| Third Law | The entropy of a perfect crystal at absolute zero (0 K) is zero |
1st Law of Thermodynamics
ΔU = Q − W
ΔU = change in internal energy · Q = heat added to system · W = work done by system
Heat Energy
Q = mcΔT
m = mass · c = specific heat capacity · ΔT = change in temperature
D. Heat Transfer Methods
Conduction, Convection, Radiation
| Method | Description | Example |
|---|---|---|
| Conduction | Heat transfer through direct contact — needs a medium; best in solids | Metal rod heated at one end |
| Convection | Heat transfer through fluid movement (liquids/gases) | Boiling water, sea breeze |
| Radiation | Heat transfer through electromagnetic waves — no medium needed | Sun heating Earth |
⚡ MCQ Tip
K = °C + 273. Boyle's = P×V constant. Charles's = V/T constant. Absolute zero = 0 K = −273°C.
First law of thermodynamics = conservation of energy (ΔU = Q − W).
PV = nRT (R = 8.314 J/mol·K).
Live Animation: Gas Particle Motion & Pressure
2D Ideal Gas — Boyle's Law Visualiser
Adjust temperature and volume — watch pressure change in real time
Pressure
Particles: 15
Avg Speed: —
Wall Hits/s: 0
Volume: —
Quick MCQ Revision
| Formula / Fact | Meaning |
|---|---|
| K = °C + 273 | Convert Celsius to Kelvin |
| °C = K − 273 | Convert Kelvin to Celsius |
| P₁V₁ = P₂V₂ | Boyle's Law — P×V = constant (fixed T) |
| V₁/T₁ = V₂/T₂ | Charles's Law — V/T = constant (fixed P) |
| P₁/T₁ = P₂/T₂ | Gay-Lussac's Law — P/T = constant (fixed V) |
| PV = nRT | Ideal Gas Law (R = 8.314 J/mol·K) |
| Q = mcΔT | Heat energy = mass × specific heat × temp change |
| ΔU = Q − W | 1st Law of Thermodynamics |
| Absolute zero | 0 K = −273°C — minimum possible temperature |
| Entropy | 2nd Law — entropy always increases in isolated systems |