Physic unit 1/2 glossary

absolute zero

The coldest possible temperature.

absorbed dose

The amount of ionising radiation absorbed per kilogram of irradiated material, measured in grays (Gy).

absorption

The taking up and storing of energy, such as radiation, light or sound, without it being reflected or transmitted.

acceleration

The rate of change of velocity, measured in m s−2.

activity

The number of nuclei of a radioactive substance that decay each second, measured in becquerels (Bq).

air pressure

The force per unit area exerted by air on an object.

air resistance

The retarding force (drag) caused by collisions between air and moving objects.

alpha particle

A particle consisting of two protons and two neutrons ejected from the nucleus of a radioactive nuclide.

alternating current

An electric current in which electrons oscillate backwards and forwards.

amplitude

The maximum displacement of a particle from the average or rest position.

angle of incidence

The angle an incident ray makes with the normal to the surface it strikes.

angle of reflection

The angle a reflected ray makes with the normal to the surface it strikes; equal to the angle of incidence.

angle of refraction

The angle a refracted ray makes with the normal as it travels from one medium to another.

antineutrino

A neutral subatomic particle that interacts very weakly with other matter.

antinode

Areas in a standing wave where complete constructive interference is happening.

artificial transmutation

The changing of one element or isotope into another.

atomic number

The number of protons in a nucleus.

background radiation

The low level of ionising radiation that exists in the environment.

beta particle

An electron or positron ejected from the nucleus of a radioactive nuclide.

binding energy

Energy required to split a nucleus into its separate nucleons.

centre of mass

A single point in an object where the mass can be considered to be concentrated.

chain reaction

A series of nuclear fissions that may be controlled or uncontrolled.

charge

A property of matter that causes electric effects; positive for protons, negative for electrons.

circuit breaker

A device that automatically switches off an excessive current.

collinear

Lying on the same straight line.

components

The components of a force are two vectors at right angles to each other.

compressions

Areas of high pressure in a wave.

conduction

The movement of energy from one object to another without the net movement of particles.

conductor

A substance that readily conducts heat, electricity, sound or light.

conservation of energy

The energy in a system before an interaction is equal to the energy in the system after the interaction.

constructive interference

The process where two or more waves combine to reinforce each other.

contact forces

Forces that exist when materials are touching each other.

control rod

Material that absorbs neutrons in a nuclear reactor.

controlled variable

A variable that must be kept constant during an investigation.

convection

A process of heat transfer through a gas or liquid by bulk motion.

conventional current

A flow of positive electric charge; opposite to electron flow.

coolant

A substance used to transfer thermal energy from the core of a nuclear reactor.

core

Part of a nuclear reactor where nuclear fission occurs.

coulomb

The SI unit of charge; 1C is the charge of approximately 6.2 × 10^18 protons.

crest

The maximum positive displacement reached in a wave.

critical angle

The incident angle at which total internal reflection occurs.

critical mass

The minimum amount of enriched fissile material that leads to a sustained fission reaction.

current

The net flow of electric charge, measured in amperes (A).

daughter nucleus

A nucleus on the product side of a nuclear equation resulting from fission or decay.

decay series

A sequence of radioactive decays that results in the formation of a stable isotope.

dependent variable

The variable that may change in response to the independent variable.

destructive interference

The process where waves combine to reduce the amplitude.

deuterium

An isotope of hydrogen with one proton and one neutron.

diffract

The process that causes a wave to spread out.

diffuse

Spread out; a wave reflecting off an irregular surface.

dimension

Space consisting of three length dimensions arranged at 90 degrees to each other.

dimensional analysis

Using units in a graph or formula to check correctness.

direct current

Electricity in which electrons travel in one direction only.

direction conventions

Standardised systems for describing travel direction.

displacement

An object’s change in position, a vector quantity.

distance travelled

How far an object travels during a motion; a scalar value.

Doppler effect

A change in the observed frequency of a wave when the source and observer are in motion relative to each other.

dose equivalent

A measure of the biological damage inflicted on a tissue due to radiation.

earth

The safety wire in electrical devices, carrying excess current into the Earth.

echo

The reflection of sound from a distant surface.

effective resistance

A single resistance that can replace multiple resistors for circuit analysis.

efficiency

The percentage of energy effectively transformed by a system.

elastic collision

Collision in which kinetic energy is conserved.

electric current

The flow of charged particles.

electric shock

Excess electricity flows into the human body due to malfunction.

electrical potential energy

Potential energy due to the separation of charge in a circuit.

electricity

A form of energy resulting from the existence of charged particles.

electromagnetic radiation

A range of frequencies created by accelerating charges.

electromagnetic spectrum

The entire range of electromagnetic radiation.

electron

A negatively charged particle in an atom.

electron flow

The net flow of electrons in a circuit.

electronvolt (eV)

A small unit of energy; 1 eV = 1.6 × 10^-19 J.

electrostatic force

A force acting between charged particles.

elementary charge

The magnitude of charge on an electron or proton.

emit

To give out energy in various forms.

energy

The ability of an object to do work.

evaporation

Changing a liquid into a gas, often due to heat.

fast breeder reactor

A nuclear reactor where some neutrons from uranium-235 are absorbed by uranium-238.

first harmonic

The longest resonant wavelength in a string or pipe.

fissile

Capable of undergoing nuclear fission after capturing low-energy neutrons.

fission

When a nucleus splits into two or more pieces.

fission fragments

Nuclides formed during nuclear fission.

forcing frequency

The frequency of the force applied to an oscillating object.

force

A vector quantity that measures the magnitude and direction of a push or pull.

free fall

Motion due only to gravity.

frequency

The rate at which something occurs, measured in hertz (Hz).

fuel rod

A long, thin rod of enriched uranium used in a nuclear reactor.

fundamental

The lowest form of vibration, with one antinode.

fuse

A device that melts and breaks the circuit when too much current flows through it.

fusion

The process where small nuclei combine to form larger nuclei.

gamma ray

High-energy electromagnetic radiation from the nucleus of a radioactive nuclide.

Geiger counter

A device for measuring radioactive emissions.

gravitational potential energy

Energy available due to position in a gravitational field.

half-life

The time taken for half of the nuclei of a radioactive isotope to decay.

harmonic

The resonant frequencies produced when standing waves are formed.

heat

Energy transferred from a hotter object to a cooler one.

heat exchanger

Part of a nuclear reactor that turns water into steam.

heavy water

Water with a higher than normal proportion of deuterium.

impulse

The change in momentum of an object.

incident

Arriving at or striking a surface, especially light or radiation.