B.1 Thermal energy transfers - Key terms

ambiguity

open to different interpretations

kinetic theory of matter

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

ions

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

atoms

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

expand

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

thermal equilibrium

all temperatures within a system are constant

thermal contact

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

Celsius (scale of temperature)

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

thermometer

an instrument for measuring temperature

Kelvin scale of 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

absolute zero

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

vibrational kinetic energy

kinetic energy due to vibration/oscillation

Boltzmann constant, k₈

important constant that links microscopic particle energies to macroscopic temperature measurements

sense perception

how we receive information, using the five human senses

conduction (thermal)

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

insulator (thermal)

a material that significantly reduces the flow of thermal energy

thermal conductivity, k

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

convection

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

emit

to send out from a source

thermal radiation

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

infrared

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

absorption

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

black body

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

black-body radiation (spectrum)

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

Stefan-Boltzmann law

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

celestial objects

any naturally occurring objects that can be observed in space

Wien’s displacement law

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

luminosity (stellar)

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

star map

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

apparent brightness, b

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

intensity, I

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

inverse square law

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)

standard candles

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

specific heat capacity, c

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

immersion heater

heater placed inside a liquid or object

lagging

thermal insulation

thermal capacity

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

calorimeter

apparatus designed for (calorimetry) experiments investigating thermal energy transfers

phase (of matter)

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

states of matter

solid, liquid or gas (or plasma)

melting

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

fusion (thermal)

melting

freeze

change from a liquid to a solid, also called solidify

evaporation

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

vaporization

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

boiling

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

condense

change from a gas or vapour to a liquid

refrigerant

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

humidity

a measure of the amount of water vapour present in air

latent heat

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

specific latent heat, Lբ or Lᵥ

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