Thermal Physics

Heat (Q)

Energy transferred due to temperature difference; unit: joule (J).

Temperature (T)

Measure of average kinetic energy of particles; unit: kelvin (K).

Absolute Zero

0 K, lowest possible temperature, minimum molecular motion.

Thermal Expansion

Increase in size of a material as temperature increases.

Ideal Gas

Particles have negligible volume and no intermolecular forces.

Kinetic Theory

Gas particles move randomly; pressure comes from collisions.

1 Calorie

Heat needed to raise 1 g of water by 1°C.

Mechanical Equivalent of Heat

1 calorie = 4.186 joules; heat and work are equivalent.

Specific Heat (c)

Heat needed to raise 1 kg of substance by 1 K; Q = mcΔT.

Heat Capacity (C)

Heat needed to raise temperature of entire object by 1 K; C = mc.

Calorimetry

Measuring heat transfer using conservation of energy; heat lost = heat gained.

Phase Change

Change of state with no temperature change.

Latent Heat (L)

Heat required for phase change; Q = mL.

Thermal Conductivity (k)

Measure of how well a material conducts heat.

Conduction

Heat transfer by direct contact; Q/t = kAΔT/L.

Convection

Heat transfer by motion of fluids.

Radiation

Heat transfer by electromagnetic waves; no medium required.

Work Done on a Gas

W = ∫P dV; area under PV curve equals work done.

First Law of Thermodynamics

ΔU = Q − W.

Internal Energy

Total microscopic kinetic and potential energy of particles.

Second Law of Thermodynamics

Entropy of an isolated system always increases.

Entropy (S)

Measure of disorder; ΔS = Qrev / T.

Ideal Gas Law

PV = nRT; R = 8.31 J/mol·K.

Isothermal Process

Temperature constant.

Adiabatic Process

No heat transfer; Q = 0.

Isobaric Process

Pressure constant.

Isochoric Process

Volume constant; W = 0.

Cyclic Process

System returns to original state; ΔU = 0.

Heat Engine

Device that converts heat into work using hot and cold reservoirs.

Thermal Efficiency

e = Wout / Qin.

Carnot Engine

Efficiency e = 1 − Tc/Th.

Blackbody

Perfect absorber and emitter of radiation; depends only on temperature.

Boltzmann Constant (kB)

1.38 × 10⁻²³ J/K; used for individual molecules.

RMS Speed

vrms = √(3kBT / m).

Relationship of R and kB

R used for moles, kB for molecules; R = NAkB.