GLossary

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GLOSSARY

acceleration (a) the time rate of change in velocity of an object, a vector quantity

amplitude the maximum displacement along a wave

animal electricity the source of electricity as proposed by Galvani arising from his experiments with frogs legs

area under the curve the area bound by the graph and the x-axis

astronomical unit (AU) the average distance between the Earth and the Sun (approx. 150 million km)

average speed the distance travelled divided by the time taken for an entire journey or segment of a journey

bandwidth the rate of data transfer

centripetal acceleration the acceleration of an object due to its circular motion directed towards the centre of the circle

Classical Physics physics based upon principles developed prior to Einsteins general theory of relativity and quantum physics

compression areas within a medium where the particles are temporarily closer together as a wave passes

constructive interference when two or more waves superpose to give a resultant wave having a larger amplitude than any of the component waves

convection currents movements of regions of hotter material usually in an upward direction away from the core of the star

conventional current the imaginary flow of positive particles or fluid around a circuit that has the opposite direction to the actual flow of electrons

crest the top of a transverse wave

critical angle (C) the angle of incidence that gives an angle of refraction of 90

current (I) the number of coulombs of electrons flowing past a point in a circuit in one second, measured in amperes (A)

destructive interference when two or more waves superpose to give a resultant wave having a smaller amplitude than any of the component waves

digital data information stored in binary form, that is, as 0s or 1s

direction of a magnetic field

the direction of the force a north pole will experience if placed within the field

direction of electric field the direction of the force experienced by a positive charge within the electric field

displacement in the context of waves, the distance a point on a wave is away from its rest position

displacement (r) in the context of velocity, the straight-line distance between two positions, with direction

elastic collisions collisions in which the kinetic energy of the system is conserved

electric field a field of force surrounding charged objects experienced by another charge placed nearby measured in newtons per coulomb (N C1 ) or volts per metre (V m1)

electromagnetic induction

the production of an electric current or potential in a conductor that experiences a changing magnetic field intensity (flux)

electromagnetic waves oscillating electric and magnetic waves that do not require a medium and travel at the speed of light in a vacuum

electron current the actual flow of electrons that constitutes an electric current

energy (E ) the ability to do work

epicycles circles within circles, used by astronomers in the past to explain the motion of heavenly bodies

fixed end an end of a spring or string that cannot move up or down as a wave is reflected

force (F ) a push or a pull exerted on an object that may cause a change in motion or shape

frame of reference an object or a coordinate system that can be used to describe or compare motions

free end an end of a spring or string that is able to move up and down with the wave as it is being reflected

frequency ( f ) the number of whole oscillations or wavelengths that pass a point per second, measured in hertz (Hz) or cycles per second

friction a force that opposes motion or the force between two objects preventing their motion by sliding

GLossary

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GLossary

geocentric Earth-centred

heliocentric Sun-centred

impulse (I ) the product of the net force acting and the time it is acting

inelastic collisions collisions in which the kinetic energy of the system is not conserved

inertia the tendency for an object to maintain its motion

instantaneous speed the speed of an object at a particular instant in time

law of conservation of momentum

the momentum of a system before a collision equals the momentum of the system after the collision if no external forces act on the system

law of inertia also known as Newtons first law: a body will retain its state of motion unless acted upon by an unbalanced force

light year (l.y.) the distance light travels in one Earth year (approx 9.4 3 1012 km)

longitudinal waves waves in which the motion of the medium is back and forth parallel to the direction of propagation of the wave

magnetic field a force field surrounding a magnetic substance such that another magnetic substance will experience a force if placed within the field

Main Sequence stars stars that are fusing hydrogen into helium within their cores

mass (m) a measure of how much matter exists in a body

mechanical waves waves that require a medium for their propagation

mechanics the study of forces and their effects on objects

medium the material that oscillates or is disturbed as a wave passes through it

metallic electricity the source of electricity as proposed by Volta arising from his experiments with different metals

modulation the variations made to the frequency or amplitude of a carrier wave containing the information

momentum (p) the product of an objects mass and velocity

net force ( F ) the vector sum of all the forces acting on an object

non-ionising radiation electromagnetic radiation with sufficiently low frequencies so as not to cause electrons to be lost from atoms upon exposure

non-ohmic conductors conductors (or resistances) that do not obey Ohms law over a given range of conditions

normal force or reaction force

the force exerted on an object perpendicular to the surface it is on or pushing against (often a component of the objects weight)

nuclear fusion the combining of two smaller nuclei to produce a larger nuclei, in the process releasing energy

Ohms law expressed as V = IR or R = VI showing the relationship between voltage across and current through a

resistance

ohmic conductors conductors (or resistances) that obey Ohms law over a given range of conditions

optical fibre cables cables containing many strands of glass fibres in which visible or infrared light can travel, trapped by the effect of total internal reflection

parallel circuit a circuit in which the resistances/devices are wired side by side so that the current can flow through them simultaneously

parsec (pc) the distance to an object having a parallax angle of one arcsecond (one second of one degree) (approx 3.26 l.y.)

period (T) the time taken for the passing of one complete oscillation or wavelength

photosphere the apparent surface of a star from where the light seems to originate

power (P) the product of the potential difference (V) and the current (I) through a device or the rate at which work (energy) is being expended

principle of superposition

the way in which, when two or more waves coincide, their displacements add to give the displacement of the resultant wave

rarefaction areas within a medium where the particles are temporarily further apart as a wave passes

red giant stars stars that have become enlarged to many times their original size and are fusing heavier elements in their cores

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refractive index (n) a relative measure of how the speed of light is slowed in a medium

resistance (R) the measure of the ability of a material to prevent the flow of electric current through it

resolving finding the two perpendicular components of a vector

scalar quantity a quantity having magnitude and no direction

series circuit a circuit in which the resistances/devices are wired end to end so that the current flows through them successively

solar wind a stream of charged particles ejected into space from the Sun

speed the distance travelled divided by the time taken

sunspots cooler regions on the surface of the Sun that appear darker than the surrounding photosphere

supernova an exploding star briefly emitting as much light as an entire galaxy

total internal reflection the reflection of light (or any other wave) within a more dense medium when the angle of incidence exceeds the critical angle

transverse waves waves in which the motion of the medium is transverse to (perpendicular to) the direction of propagation of the wave

trough the bottom of a transverse wave

uniform circular motion motion in a circle with constant (uniform) speed

vector quantity a quantity having both magnitude and direction that can be represented by an arrow

velocity (v) in the context of waves, the speed with which a wave propagates (travels). In the context of motion, speed with direction indicated

voltage/potential difference (V )

a measure of how many joules of energy are expended by each coulomb of electrons flowing through that part of a circuit or the difference in energy of each coulomb of electrons between different points around a circuit

wavebands ranges of wavelengths of radiation within the electromagnetic spectrum having common uses due to their common characteristics

wavelength () the distance between two successive corresponding points on a wave

weight (W ) the force exerted on a mass due to the gravitational field

white dwarf stars stars at the end of their life cycles that are no longer fusing nuclei in their cores but continue to emit light due to their residual heat

work (W ) the transfer of energy causing a change in an objects energy