A-Level Physics OCR A Definitions

acceleration

Rate of change of velocity. Vector quantity

Acceleration of free fall

Rate of change of velocity of object falling in a gravitational field

air resistance

Drag/resistive force experienced by objects moving through air

Ammeter

Device used to measure electric current-placed in series (ideally 0 resistance)

ampère

Base SI unit of electric current, A, current flowing in two parallel wires in a vacuum 1m apart such that atractive force 2.0*10-7 per metre length of wire between them

amplitude

Max displacement from equlibrium point of a particle in a wave

angle of incidence

Angle between direction of travel of incident ray and normal

angle of reflection

angle between direction of travel of reflected ray and normal

anion

negatively charged ion -attracted to anode

antiparallel

Same line but opposite directions

antiphase

Particles ocillating where one reaches max displ. whilst other reaches min displ.

Archimedes' Principle

Upthrust on a object in fluid equals weight of fluid it displaces

average speed

Rate of change of distance in time

average velocity

rate of change of displacement in time

base unit

one of 7 units that form building blocks of SI measurements

battery

collection of cells that transfer chemical energy to electrical energy

braking distance

distance travelled by vehicle from time brakes applied to full stop

breaking strength

stress value at point of fracture-breaking force diveded by cross sectional area

brittle

lack of ability of plasticity

capacitor

compenent that stores charge, consists of 2 plates seperated by an insulator

cathode

negatively charge electrode

cation

posiively charge ion that is attracted to cathode

cell

device that transfers chemical energy into electrical energy

centre of gravity

imaginary point at which entire weight of object appears to act

centre of mass

point through which any fexternal force applied makes straight line motion but no rotation

charge carrier

particle with charge that moves through material to form electric current

closed system

isolated system that has no interaction with surroundings

coherence

two waves that are coherent have same constant phase difference

compression

a region in which medium is denser or has higher pressure than surrounding medium

compressive deformation

change in shape of object due to compressive forces

compressive force

2 or more forces acting together that reduce length of volume of object

conservation of charge

Law where electric charge can neither be created nor destroyed-total charge must be same before and after interaction

constant speed

motion in which distance per unit time is same

constant velocity

motion where change in displacement per time stays same

constructive interference

superposition of 2 waves in phase so resultant wave has greater amplitude than original waves

conventional current

model used to describe electric current in a circuit-conventional current travels from positive to negative-but doesnt actually

coulomb

derived SI unit of electric charge, 1 coulombs passes a point in one second. 1C=1As

couple

pair of equal but opposite forces acting on a body but not in straight line

critical angle

angle of incidence at boundary between 2 media will product an angle of refraction of 90 degrees

crystallography

method for determining structure of substance by studying interference patterns produced by waves passing through a crystal of substance

de Broglie equation

equation relating wavelength and momentum of a particle

density

mass per unit volume of a substance

derived quantity

quantity that comes from base units

destructive interference

superposition of 2 waves in antiphase so the waves cancel each other out and resultant wave has smaller amplitude than original waves

diffreaction

phenomenon of waves passing through a gap or around an obstacle spread out

diode

semiconductor component that allows current only in one direction

displacement

distance travelled in particular direction-vector with magnitude and direction

displacement (waves)

distance from equilibrium position in particular direction

drag force

resistive force exerted by a fluid on an object moving through it

ductile

property of a material that has large plastic region in a stress-strain graph

efficiency

ration of useful output energy to total input energy (%)

elastic deformation

reversible change in shape of object due to compressive or tensile force-removal of stress or force will return the object to original shape and size

elastic limit

value of stress or force beyond which elastic deformation becomes plastic deformation-object will not return to original shape or size after force released

elastic potential energy

energy stored in a object due to its deformation

electric charge

(Q)physical property + or - measured in coulombs C

electricity meter

device that measures electrical energy supplied in kWh to a house from the grid

electrolyte

liquid containing ions that are free to move so conduct electricity

electromagnetic spectrum

full range of frequencies of electromagnetic waves

electromotive force (e.m.f)

work done on charge carriers per unit charge (V) measured accross a cell, battery or power supply

electron gun

device that uses accelerating potential difference to produce beam of electrons

electronvolt

derived unit of energy-subatomic particles and photons. Energy transferred to/from electron when passes through P.D of 1V. 1eV = 1.6*10-19

elementary charge

smallest sum of electric charge. 1.6*10-19

energy

capacity for doing work Joules

equilibrium

when body in equilibrium, net force and moment acting are 0

equilibrium pos (waves)

resting position for particles in medium

extension

increase in length of object when tensile force exerted

filament lamp

electrical component containing filament of wire converting electrical to light

fluid

substance that can flow-liquids and gases

force

push or pull on object N

force constant

quantity for dividing force by extension for object obeying hookes law

force-extension graph

force against extension with area under graph=work done on material

force-time graph

graph of net force against time, area under graph = to impulse

free electron

electron in metal not bound to atom-delocalised

free fall

motion of object accelerating under gravity with no other force acting

free-body diagram

represents all forces acting on single object

frequency(waves)

number of wavelengths passing a point per unit time

fundamental frequency

lowest frequency at which object can vibrate

fundamental mode of vibration

vibration at fundamental frequency

gamma rays

short-wavelength electromagnetic waves 10-10m to 10-16m

gold leaf electroscope

device with metallic stem and gold leaf used to measure electric charge used to be used as voltmeter for high voltages

gradient

change in vertical axis quantity divided by corresponding change in horizontal axis quantity

GPE

capacity for object doing work as result of objects position in gravitational field

harmonic

whole number multiple of fundamental frequency

Hooke's law

force applied is directly proportional to extention of spring unless limit of proportionality is exceeded

hysteresis loop

loop shaped plot obtained when loading or unloading material produces different deformations

impulse

area under force time graph-product of force and time for which force acts

in phase

particles oscillating perfectly in time and position with each other

inelastic collision

collision in which kinetic energy is lost

infrared waves

electromagnetic waves with wavelengths 10-3m to 10-7m

instantaneous speed

speed at moment it is measured-speed over infinitely small time interval

intensity(waves)

radiant power passing through surface per unit area

interference

superposition of 2 progressive waves from coherent sources to product a resultant wave with displacement equal to sum of indiv. displ. of waves

interference pattern

pattern of constructive and desctructive interference formed as waves overlap

internal resistance

reistance of a source of e.m.f.-causes loss in energy/voltage as charge passes through source

ion

atom has either lost of grained electrons so has net charge

ionic solution

ionic compound dissolved in liquid to form electrolyte

I-V characteristic

description of relationship between electric current in component and p.d. accross it. I again V graph

kilowatt-hour

derived unit energy-1kWh=3.6MJ. Energy in kWh can be calculated by multiplying power by time

kinetic energy

energy associated with object as result of its motion

Kirchhoff's first law

at any point in electrical circuit, sum of currents into that point is equal to sum of currents out of that point. Electrical charge is conserved