IGCSE - Physics summary

thinking distance

distance travelled from the point of seeing danger to the point where brakes are applied

braking distance

distance travelled from activating the breaks to stopping

speed

how far something moves every second

terminal velocity

when two forces acting upon an object are equal and balanced

when an object is travelling at a constant distance

when there is no resultant force so zero acceleration

hookes law

within the limit of proportionality, the force added is directly proportional to the extension

elastic behaviour

ability of a material that can return to its normal shape after forces that caused stretching have been removed

elastic limit

when force is removed the spring will return to its original length

newtons 3rd law

every action has its equal and opposite action

principle of moments

for an object to balance, the anticlockwise moments must equal to clockwise moments

centre of gravity/ centre of mass

point which we all assume all the mass of an object is concentrated

current

rate of flow of charge

resistance

anything which slows the flow of charge

ohms law

at constant temperature, the voltage given to a component will be directly proportional to the current through a component

live wire

carries potential difference to the device

neutral wire

completes the circuit

earth wire

takes current to ground when there is a fault

fuse

wire that melts when there is a fault

direct current

current flowing in the same direction from positive to negative

alternating current

current that continuously changes its direction, going back and forth around a circuit

insulator

any material that doesn’t allow electric current to pass through it easily

what remains constant during refraction

frequency

what remains constant during doppler effect

speed

electrostatic phenomena

when static electricity has specific effect

spark

sudden, rapid flow of electric charge through the air

longitudinal waves

vibrations are parallel to direction of energy transfer

traverse waves

vibrations are perpendicular to energy transfer

amplitude

max displaceent from equilibrium position in a wave

wavefront

moving line that joins all the points on the crest of the wave

frequency

no of waves passing a point per second

wavelength

distance between same points of successive waves

wave properties

transfer energy and information without transferring matter

all waves travel at same speed in free space

refraction

when light changes speed as it changes medium

reflection

when angle of incidence = angle of reflection

critical angle

angle of incidence inside the optically denser medium and results in an angle of refraction

human hearing range

20-20,000Hz

total internal reflection

when light ray is completely reflected inside a denser medium with no light escaping across the boundary

cathode ray oscilloscope

instrument which changes sound into an electrical signal so it can be displayed on a screen and analysed

doppler effect

apparent change in the frequency and wavelength of a wave when there is a relative motion between wave source and observer

pressure

Pa or N/m²

evaporation

escape of most energetic molecules fom the surface of the liquid, occuring at a temp below b.p

specific heat capacity

energy required to change temp of object by 1 degrees celcius per kg of mass

boyles law

for a fixed mass of gas at a constant temp, the pressure of the gas is inversely proportional to its volume

pressure law

for a fixed mass of gas at a constant volume, pressure is directly proportional to its temp (kelvin)

absolute zero

theorised temperature where all movement of atoms has stopped

magnetic field line

shows direction a free north pole would move in

split ring commutator

reverses direction of current every half-turn so motor coil rotates continuously in one direction

step-up transformer

device used to increase an alternating voltage from primary to secondary circuit

mass of electron

1/1800

radioactive decay

random event where unstable nucleus emits radiation (high energy particle/wave) to become more stable

radioactive

atomic nuclei are unstable and radioactive (imbalance of protons/neutrons)

activity

rate at which source decays

half life

time it takes for activity of radioactive sample to halve

ionising ability

how easily it ionises other atoms

irradiation

exposure to radioactive source outside the body

contamination

unwanted presence of materials containing radioactive atoms on or inside an object/person

background radiation

low level ionising radiation that is produced al the time

photons

packets of energy which emit gamma radiation

chain reaction

neutrons released by a fission reaction strike other nuclei, triggering further fission reactions

nuclear fusion

joining together of two smaller lighter nuclei to form a larger heavier nucleus, releasing energy

conduction

heat transferred by vibration of particles in lattice

convection

transfer of thermal energy in fluids through the movement of the particles themselves

radiation

transfer of thermal energy by infrared e.m waves without the need for particles/medium

law of conservation of energy

energy cant be made/destroyed

work

force applied over a distance to move an object

power

rate of transfer of energy

renewable source

energy source that is replenished at a faster rate than rate it is being used

universe

large collection of billions of galaxies

galaxy

large collection of billions of stars

solar system

sun + all objects that orbit it

planet

object that orbits a star

dwarf planet

object orbiting star that doesn’t have enough gravity to clear its path of debris

orbit

path of object in space

moon

natural satellite that orbits a planet

comet

object with elliptical orbit around sun

artificial satellite

man-made object orbiting around planet which transmits info to earth

relationship between gravitational field strength and mass of planet

bigger the planet, higher the strength

hertzprung russel diagram

relationship between luminosity/brightness and temp

apparent magnitude

the brightness of a star as seen from earth

absolute magnitude

apparent magnitude a star would have if it were placed at standard distance of 10 parsecs away from earth

bing bang theory

all matter created at beginning of universe, 13.5m years ago