Fundamentals of Thermodynamics and Wave Physics

Thermodynamics Fundamentals

Heat

Energy transferred from one body to another due to a temperature difference. Heat is energy in transit or motion.

Work and Calories

Different units for measuring energy transfer between two bodies.

Temperature

A measure of the average kinetic energy of the particles that constitute a body.

Internal Energy

The sum of the kinetic and potential energies of all the particles that make up a body.

Thermometric Scales

Relationships between different temperature scales include: T(°C)/100 = (T(°F) - 32)/180, and T(K) = T(°C) + 273.15.

Thermal Equilibrium

Two bodies are in thermal equilibrium when they are at the same temperature.

Mechanical Equivalent of Heat

The relationship between Joules (J) and calories (cal): 1 cal ≈ 4.18 J; 1 J ≈ 0.24 cal.

Heat Transfer (Temperature Change)

The energy (Q) absorbed or released by a body during a temperature change depends on its mass (m), specific heat (c), and the temperature change (ΔT): Q = mcΔT.

Heat Transfer (Phase Change)

A change of state (e.g., melting, boiling) occurs at a constant temperature. The energy (Q) transferred depends on the mass (m) and the latent heat (L) of the phase change: Q = mL.

Thermal Expansion

Increasing temperature generally increases particle speed and average separation, causing the body to expand.

Conservation of Energy

Energy is conserved; it is neither created nor destroyed, only transformed. However, with each transformation, energy tends to become less useful (related to an increase in entropy).

Heat Engines

Devices that convert thermal energy (heat, Q_H) partially into work (W). Their efficiency (η) is typically less than 1: η = W / Q_H = (Q_H - Q_C) / Q_H, where Q_C is the heat rejected.

Wave Properties

Wave

A disturbance, often originating from a vibration, that propagates through space, transferring energy without transporting matter.

Wave Energy

The energy transported by a wave is directly proportional to the square of its amplitude and the square of its frequency.

Mechanical Waves

Require a material medium for propagation; they cannot travel through a vacuum.

Electromagnetic Waves

Can propagate through a vacuum, where they travel at the speed of light (c), faster than in any material medium.

Longitudinal Waves

The particle vibration direction is parallel to the wave propagation direction (e.g., sound waves in air).

Transverse Waves

The particle vibration is perpendicular to the wave propagation direction (e.g., light waves, waves on a string).