B.1 Thermal energy transfers - Key terms

open to different interpretations

all matter is composed of a very large number of small particles that are in constant motion

an atom or molecule that has gained or lost one or more electrons

the particles from which chemical elements are composed, they contain subatomic particles

increasing in size, an expansion of a gas is an increase in volume

all temperatures within a system are constant

objects can be considered to be in thermal contact if thermal energy (of any kind) can be transferred between them

temperature scale based on the melting point (0°C) and boiling point (100°C) of pure water

an instrument for measuring temperature

also known as the absolute temperature scale, temperature scale based on absolute zero (0 K) and the melting point of water (273 K), the kelvin, K, is the fundamental SI unit of temperature, T (in K) = 0°C + 273

temperature at which (almost) all molecular motion has stopped (0 K or -273°C)

kinetic energy due to vibration/oscillation

important constant that links microscopic particle energies to macroscopic temperature measurements

how we receive information, using the five human senses

passage of thermal energy through a substance as energy is transferred from particle to particle

a material that significantly reduces the flow of thermal energy

constant that represents the ability of a substance to conduct thermal energy

passage of thermal energy through liquids and gases due to movement of the substance because of differences in density

to send out from a source

electromagnetic radiation emitted because of the movement of charged particles in the atoms of all matter at all temperatures, most commonly, infrared

electromagnetic radiation emitted by all objects (depending on temperature) with wavelengths longer than visible light

when the energy of incident particles or radiation is transferred to other forms within a material

an idealized object that absorbs all the electromagnetic radiation that falls upon it, a perfect black body also emits the maximum possible radiation

radiation emitted from a “perfect” emitter, the characteristic ranges of different radiations emitted at different temperatures are commonly shown in graphs of intensity against wavelength

an equation that can be used to calculate the total power radiated from the surface of a black body, P = σAT⁴, σ is known as the Stefan-Boltzmann constant

any naturally occurring objects that can be observed in space

relationship between absolute temperature and the wavelength emitted with maximum power by a black body at that temperature

total power of electromagnetic radiation emitted by a star (SI unit: W)

two-dimensional representation of the relative positions of stars as seen from Earth

intensity (power/area) of radiation received on Earth from a star (SI unit: Wm⁻²)

wave power/area: I = P/A (SI unit: Wm⁻²)

for waves/energy/particles/fields spreading equally in all directions from a point source without absorption or scattering, the intensity is inversely proportional to the distance squared, I ∝ 1/x² (Ix² = constant)

term used by astronomers to describe the fact that the distance to a galaxy can be estimated from a knowledge of the luminosty of a certain kind of star within it

the amount of energy needed to raise the temperature of 1 kg of a substance by 1 K

heater placed inside a liquid or object

thermal insulation

the amount of energy needed to raise the temperature of a particular object by 1 kelvin

apparatus designed for (calorimetry) experiments investigating thermal energy transfers

a substance in which all the physical and chemical properties are uniform, in physics, the term phase change is used to describe changes between solids, liquids and gases of the same substance

solid, liquid or gas (or plasma)

change from a solid to a liquid, usually at a specific temperature (melting point)

melting

change from a liquid to a solid, also called solidify

the change from a liquid to a gas (vapour) at any temperature below the boiling point of the liquid, occurs only at the liquid surface

change from a liquid to a vapour (gas) by boiling or evaporation, a vapour is a gas which can be condensed by pressure

change from a liquid to a gas/vapour throughout the liquid at a precise temperature

change from a gas or vapour to a liquid

fluid used in the refrigeration cycle of refrigerators, air conditioners and heat pumps

a measure of the amount of water vapour present in air

thermal energy that is transferred at constant temperature during any change of physical phase

the amount of energy needed to melt (fusion) or vaporize 1 kg of a substance at constant temperature