Physics B.1 Thermal Energy Transfers

Molecular theory:

Molecular theory describes the behavior of matter in terms of the motion and interactions of its constituent particles, such as atoms and molecules. It provides a microscopic explanation for the macroscopic properties of solids, liquids, and gases.

Density:

Density is the mass per unit volume of a substance. It is given by ρ = m / V, where ρ is the density, m is the mass, and V is the volume.

Temperature:

Temperature is a measure of the average kinetic energy of the particles in a substance. It is typically measured in degrees Celsius (°C) or Kelvin (K), with the relationship between the two scales given by T(K) = T(°C) + 273.

Internal energy:

Internal energy is the total energy of a system due to the kinetic and potential energies of its particles. It includes the random kinetic energy of the particles and the intermolecular potential energy.

Phase change:

A phase change is a transition of a substance from one state of matter to another, such as from solid to liquid or liquid to gas. It involves a change in the energy of the substance at a constant temperature.

Specific heat capacity:

Specific heat capacity is the amount of heat energy required to raise the temperature of a unit mass of a substance by one degree Celsius or Kelvin. It is given by c = Q / (mΔT), where Q is the heat energy, m is the mass, and ΔT is the change in temperature.

Specific latent heat:

Specific latent heat is the amount of heat energy required to change the phase of a unit mass of a substance without a change in temperature. It is given by L = Q / m, where Q is the heat energy and m is the mass.

Conduction:

Conduction is the transfer of thermal energy through a material without the movement of the material itself. It occurs due to the transfer of kinetic energy between particles in direct contact.

Convection:

Convection is the transfer of thermal energy by the movement of a fluid. It occurs due to the differences in density within the fluid, causing warmer, less dense fluid to rise and cooler, denser fluid to sink.

Thermal radiation:

Thermal radiation is the transfer of thermal energy by electromagnetic waves. It does not require a medium and can occur through a vacuum.

Stefan-Boltzmann law:

The Stefan-Boltzmann law states that the total energy radiated per unit surface area of a black body is proportional to the fourth power of its absolute temperature. It is given by L = σAT⁴, where L is the luminosity, A is the surface area, T is the absolute temperature, and σ is the Stefan-Boltzmann constant.

Apparent brightness:

Apparent brightness is the amount of energy received per unit time per unit area from a light source. It is given by b = L / (4πd²), where b is the apparent brightness, L is the luminosity of the source, and d is the distance to the source.

Luminosity:

Luminosity is the total amount of energy emitted per unit time by a light source. It is typically measured in watts (W).

Emission spectrum:

An emission spectrum is the distribution of electromagnetic radiation emitted by a substance when it is excited. It provides information about the energy levels of the substance’s atoms or molecules.

Wien’s displacement law:

Wien’s displacement law states that the wavelength at which the intensity of radiation from a black body is at its maximum is inversely proportional to the absolute temperature of the body. It is given by λmaxT = 2.9 × 10⁻³ mK, where λmax is the peak wavelength and T is the absolute temperature.