acceleration the rate of increase of velocity
alpha particle a fast moving helium nucleus that is emitted from the nucleus of an atom in radioactive decay; consists of two protons and two neutrons
alternating current (a.c.) a current that flows in one direction and then the other, continually reversing
ammeter an electrical meter used for measuring current
ampere (A) the unit of electric current
amplitude the maximum displacement of an oscillating particle from its mean position
analogue signal an analogue signal has a shape that corresponds to the shape of the signal being carried
AND-gate a logic gate that gives a high output when both its inputs are high
angle of incidence the angle between an incident ray and the normal
angle of reflection the angle between a reflected ray and the normal
angle of refraction the angle between a refracted ray and the normal
atom the smallest part of an element that still has the properties of that element
background radiation radiation caused by radioactive isotopes in the surroundings
balanced forces forces whose effects cancel out
barometer an instrument used to measure atmospheric pressure
battery two or more cells connected in either series or parallel
bequerel (Bq) the unit of activity = 1 event per second
beta particle a very fast moving electron emitted from the nucleus of an atom during radioactive decay
boiling the process by which vapour bubbles form in the body of a liquid when the liquid is converted to a vapour at a fixed temperature
Brownian movement the random zigzag movement of particles caused by their bombardment by molecules
capacitor an electronic device that stores electric charge
cathode ray oscilloscope a device used to show the pattern of rapidly changing potential differences
cathode rays a beam of electrons that have been accelerated through a few hundred volts
centre of mass the point at which all the mass of a body may be considered to be concentrated
centripetal acceleration the acceleration of a body towards the centre of the circle around which it is travelling
centripetal force the force on a body towards the centre of the circle around which it is travelling
cloud chamber a device that detects and shows the paths of radioactive emissions
compression a region of pressure above atmospheric pressure in a sound wave
condensation the conversion of vapour to liquid
conduction (electrical) the movement of electric charge through a body
conduction (thermal) the movement of internal energy through a body
conductor (electrical) a substance that allows electric current through it
conductor (thermal) a substance that allows the flow of internal energy through it
convection the process by which internal energy is transferred by a fluid forming a convection current
convection current the rising of a body of warm fluid (or falling of a cool fluid) owing to its expansion (or contraction) as it is heated (or cooled)
conventional current the flow of positive electric charge
coulomb (C) the unit of electric charge
critical angle the largest angle of incidence at which a ray of light can strike an interface between a dense and a rare medium and will leave the dense medium
current a flow of electric charge
diffraction the bending of a wave as it goes through a narrow gap or around a small object
digital signal a digital signal carries information in the form of a string of on and off pulses
diode an electronic component that allows current to flow in one direction only
direct current (d.c.) a current that flows in one direction only
dispersion the splitting of white light into the colours of the spectrum
earthed connected to the Earth by an electrical conductor so a current can flow to earth
efficiency the proportion of the energy supplied to a device that is transformed into useful energy output
elastic a material that returns to its original shape when a distorting force is removed
elastic potential energy energy stored by an object when it is stretched or squashed
electromagnet a magnet formed by passing an electric current through a coil of wire
electromagnetic induction the process by which an emf is generated when a conductor cuts a magnetic field
electromagnetic spectrum a family of radiation that travels at 3 x 108 m/s in a vacuum
electrostatic charge a property of some particles that causes them to attract or repel each other, it can be positive or negative
electrostatic force force exerted by one electrically-charged object on another
emf the total work done when unit charge moves around a complete circuit
energy the ability to do work
evaporation the change of liquid to vapour when molecules leave the surface of the liquid