IGCSE Physics

a.c generator

A device, such as a dynamo, used to generate alternating current (a.c)

acceleration

The rate of change of an object's velocity

acceleration due to gravity

The acceleration of an object falling freely under gravity

activity

The rate at which nuclei decay in a sample of a radioactive substance

air Resistence

The frictional force on an object moving through air

alpha decay

The decay of a radioactive nucleus by emission of an a-particle

alpha particle (a-particle)

A particle of two protons and two neutrons emitted by an atomic nucleus during radioactive decay

alternating current (a.c)

Electric current that flows first one way, then the other, in a circuit

ammeter

A meter for measuring electric current

amp, ampere (A)

The SI unit of electric current

amplitude

The greatest height of a wave above its undisturbed level

angle of incidence

The angle between an incident ray and the normal to the surface at the point where it meets a surface

angle of reflection

The angle between a reflected ray and the normal to the surface at the point where it meets a surface

angle of refraction

The angle between a refracted ray and the normal to the surface at the point where it passes from one material to another

average speed

Speed calculated from total distance travelled divided by total time taken

axis

The line passing through the centre of the lens, perpendicular to its surface

background radiation

The radiation from the environment to which we are exposed all the time

barometer

An instrument used to measure atmospheric pressure

battery

Two or more electrical cells connected together in series; the word may also be sued to mean a single cell

becquerel (Bq

The SI unit of activity; 1 Bq = one decay per second

beta decay

The decay of a radioactive nucleus by emission of a beta particle

beta particle

A particle (an electron) emitted by an atomic nucleus during radioactive decay

biomass fuel

A material, recently living, used as a fuel

boiling point

The temperature at which a liquid changes to a gas (at constant pressure)

Boyle's law

The law that relates the pressure and volume of a fixed mass of gas

brownian motion

The motion of small particles suspended in a liquid or gas, caused by molecular bombardment

cc

A device that provides a voltage in a circuit by means of a chemical reaction

centre of mass

The point at which the mass of an object can be considered to be concentrated

chemical energy

Energy stored in chemical substances and which can be released in a chemical reaction

circuit breaker

A safety device that automatically switches off a circuit when the current becomes too high

commutator

A device used to allow current to flow to and from the coil of a d.c. motor or generator

compression

A region of a sound wave where the particles are pushed close together

conduction

The transfer of heat energy or electrical energy through a material without the material itself moving

conductor

A substance that transmits heat or allows an electric current to pass through it

contaminated

When an object has acquired some unwanted radioactive substance

convection

The transfer of heat energy through a material by movement of the material itself

converging lens

A lens that causes rays of light parallel to the axis to converge at the principal focus

corkscrew rule

The rule used to determine the direction of the magnetic field around an electric current

coulomb (C)

The SI unit of electric charge; 1 C = 1 A s

count rate

The number of decaying radioactive atoms detected each second (minute or hour)

crest

The highest point of a wave

critical angle

The minimum angle of incidence at which total internal reflection occurs

current

the rate at which electric charge passes a point in a circuit

current-voltage characteristics

a graph showing how the current in a component depends on the p.d. across it

demagnetisation

destroying the magnetisation of a piece of material

density

the radio of mass to volume for a substance

diffraction

when a wave spreads out as it travels through a gap or past the edge of an object

diode

an electrical component that allows electric current to flow in one direction only

direct current (d.c)

electric current that flows in the same direction all the time

dispersion

the separation of different wavelengths of light because they are refracted through different angles

diverging lens

a lens that causes rays of light parallel to the axis to diverge from the principal focus

doing work

transferring energy by means of a force

drag

the frictional force when an object moves through a fluid (a liquid or gas)

dynamo effect

electricity is generated when a coil moves near a magnet

earthed

when the case of an electrical appliance is connected to the earth wire (for safety)

efficiency

the fraction of energy that is converted into a useful form

electric field

a region of space in which an electric charge will feel a force

electrical energy

energy transferred by an electric current

electomagnetic spectrum

the family of radiations similar to light

electron

a negatively charged particle, smaller than an atom

electron charge

the electric charge of a single electron

electrostatic charge

a property of an object that causes it to attract or repel other objects with charge

e.m.f. (electro-motive force)

the voltage across the terminals of a source of electrical energy (for example, a cell or power supply)

energy

the capacity to do work

equilibrium

when no net force and no net moment act on a body

evaporation

when a liquid changes to a gas at a temperature below its boiling point

extension

the increase in length of a spring when a load is attached

Fleming's left-hand rule

a rule that gives the relationship between the directions of force, field and current when a current flows across a magnetic field

Fleming's right-hand rule

a rule that gives the relationship between the directions of force, field and current when a current is induced by moving a conductor relative to a magnetic field

focal length

the distance from the centre of a lens to its principal focus

force

the action of one body on a second body that causes its velocity to change

fossil fuel

a material, formed from long-dead material used as a fuel

frequency

the number of vibrations per second, or number of waves per second passing a point

friction

the force that acts to prevent excessive currents flowing in a circuit

fuse

a device used to prevent excessive currents flowing in a circuit

gamma ray (y-ray)

electomagnetic radiation emitted by an atomic nucleus during radioactive decay

geothermal energy

The energy stored in hot rocks underground

gravitational potential energy (g.p.e.)

the energy of an object raised up against the force of gravity

gravity

the force that exists between any two objects with mass

half-life

the average time taken for half the atoms in a sample of a radioactive material to decay

hard

a material that, once magnetised, is difficult to demagnetise

Hooke's law

the extension of an object is proportional to the load producing it, providing that the limit of proportionality is not exceeded

image

what we see when we view an object by means of reflected or refracted rays

impulse

the product of force and the time for which it acts (impulse = Ft)

incident ray

a ray of light striking a surface

induction

a method of giving an object an electric charge without making contact with another charged object

infrared radiation

electromagnetic radiation whose wavelength is greater than that of visible light; sometimes known as heat radiation

infrasound

sound waves whose frequency is so low that they cannot be heard

insulator

a substance that transmits heat very poorly or does not conduct electricity

internal energy

the energy of an object; the total kinetic and potential energies of its particles

interrupt card

a piece of card that breaks the light beam of a light gate

ionisation

when a particle (atom or molecule) becomes electrically charged by losing or gaining electrons

ionising radiation

radiation, for example from radioactive substances, that causes ionisation

irradiated

when an object has been exposed to radiation

isotope

isotopes of an element have the same proton number buy different nucleon numbers

joule (J)

the SI unit of work or energy

kinetic energy (k.e.)

the energy of a moving object

kinetic model of matter

a model in which matter consists of molecules in motion

lamina

a flat object of uniform thinkness

laser

a device for producing a narrow beam of light of a single colour or wavelength