PHYSICS IGCSE EDEXCEL ALL PAPER 1

speed

distance/time

acceleration

change in velocity/time taken

speed in a distance time graph

gradient

acceleration in a velocity time graph

gradient

distance in a velocity time graph

area

weight

mass x gravitational field strength

scalar

magnitude only

vector

magnitude and direction

friction

force that opposes motion, present if an objet is in motion

stopping distance

thinking distance + braking distance

• faster speed increases both

• larger mass increases braking distance

• slower reaction time increases thinking distance

• increased grip decreased braking distance

terminal velocity

weight is equal to drag meaning resultant force is zero, therefore acceleration is 0

hooke’s law

extension of a helical spring is direction proportional to the applied force

• there is an elastic limit where elastic behaviour turns into plastic behaviour

• elastic behaviour: if the applied force is removed, the object will return back to its original shape

• plastic behaviour: if the applied force is removed, the object will not return back to its original shape, therefore it is deformed

newton’s laws of motion

1. if resultant force on an object = 0, it will remain at its current velocity (incl. 0 – standing still)

   • inertia means no resultant force/ object will continue doing what it’s doing

   • zero acceleration

2. object accelerates in the direction of the resultant force

   • speed can remain constant but direction changes, meaning a changed velocity

3. if object A exerts a force on object B, then object B exerts an equal and opposite force on object A

   • requirements: 1) same type of force, 2) acts on two different objects

moments

• moment = force x perpendicular distance from pivot

• newton metres = newtons x metres

• principle of moments: sum of clockwise moments equals sum of anticlockwise moments in order for a lever to be in equilibrium

• in order for lever to be in equilibrium, f1x = f2y

insulation

to stop the flow of electricity

conduction

to allow the flow of electricity

double insulation

covering a metal object in plastic, therefore it acts as an insulator

earthing

carries excess current into the earth through a metal rod put into earth

circuit breakers

switch opens, therefore breaking the circuit if too much current is flowing through

• benefit: reusable

mains electricity

230V

fuse

melts if current gets too high therefore breaking the circuit

• drawback: one time use; after it melts it must be replaced

ammeter

measures current, must be placed in series

voltmeter

measures voltage, must be placed in parallel around the component under test

a.c. supply

current is constantly changing direction

d.c. supply

current keeps flowing in the same direction

voltage

current x resistance

metal filament lamp

as temperature increases, resistance increases

wire

current through a wire is proportional to voltage

diode

current in a diode only flows through in one direction

LEDs

emit light when current flows through them in the forward direction

• used in remote controls, digital clocks, traffic lights

• don’t have a filament that can burn out

LDRs

changes resistance depending on how much light falls on it

• in bright light, resistance decreases

• in darkness, resistance increases

thermistors

temperature-dependent resistor

• in hot conditions, resistance decreases

• in cool conditions, resistance increases

series circuits

• in series, voltage is split between components

  • E.g. power source is 6V, both lightbulbs have 3V (assuming they have the same resistance)

• the current is the same everywhere in a series circuit

• benefit: more simple (less wires required)

• negative: components have a greater resistance

parallel circuits

• in parallel, voltage is equal in components

  • E.g. power source is 6V, both lightbulbs have 6V (assuming they have the same resistance)

• at a junction, current is conserved

  • current is split between branches in a parallel circuit

• benefit: if one component breaks, the others will continue running

• negative: while the bulbs may be brighter, the power source would drain faster

current

• current = charge/time

• definition: rate of flow of charge

• current is conserved at a junction

voltage

• voltage = energy/charge

• definition: energy transferred per charge

• 1 volt = 1 joule/coulomb

transverse waves

vibrations perpendicular to energy transfer

longitudinal waves

vibrations parallel to energy transfer

wave speed

λ x frequency

frequency

1/time

doppler effect

• wavefronts are further apart, therefore meaning a longer wavelength

• wavelength is inversely proportional to frequency

• longer wavelength means a lower frequency, meaning a lower pitch

• wave speed is constant

• V = λf, if wavelength is longer so frequency must be lower to maintain the same wave speed

refraction

when a wave passes a boundary between two different density media, it changes speed and sometimes direction too

• from more to less optically dense, wave goes away from the normal

• from less to more optically dense, wave goes towards the normal

electromagnetic spectrum

radio waves → microwaves → infrared → visible light → ultraviolet → x-rays → gamma rays (increasing f, decreasing λ)

radio waves -> communication

microwaves -> cell phones, however heats internal tissues

infrared -> cooking food, night vision/thermal imaging, however can cause skin burns

visible light -> photography

ultraviolet -> testing fake bank notes, sterilisation, however may cause skin cancer by the mutation of skin cells

x-rays -> view internal structure of our bodies, however may cause cancer by the mutation of cells

gamma rays -> sterilise medical equipment, however may cause cancer by the mutation of cells

graphical method

1. take multiple incidences and refractions,

2. plot a graph of sin (i) against sin (r)

3. draw a straight line of best fit (should be directly proportional)

4. find gradient of line

5. to find n, gradient = diff in y/ diff in x

critical angle

• if incidence is greater than C, all rays will be totally internally reflected

• MUST take place at a boundary from a substance that is more optically dense to a substance that is less optically dense

total internal reflection

sound waves

• humans can only hear sound waves from 20 – 20,000 Hz

• sound waves are longitudinal waves

energy stores

kinetic, thermal, chemical, gravitational potential, elastic potential, electrostatic, magnetic, nuclear

principle of conservation of energy

energy can be stored, transferred between stores or dissipated - but it can never be created or destroyed

efficiency

useful/total x 100

sankey diagrams

radiation energy transfer

• thermal radiation is infrared radiation consisting of plenty of EM waves

• an object that is hotter than its surroundings emits more radiation than it absorbs

• an object that is cooler than its surroundings absorbs more radiation than it emits

conduction energy transfer

• mainly in solids

• vibrating particles transfer energy from their kinetic energy store to the kinetic energy store of neighbouring particles

convection energy transfer

• in liquids and gases

• more energetic particles move from a hotter region to a cooler region, transferring energy as they do

• convection currents are all about changes in density

colours in energy transfer

black → good absorber, bad reflector

white → good reflector, bad absorber

matte → good absorber

shiny → good reflector

work done

force x distance moved

kinetic energy store

KE = ½ x mass x speed²

density

mass/volume

pressure

force/area

absolute zero

-273 degrees celsius

particle collision theory

colliding gas particles create pressure

• as gas particles move, they randomly collide into each other

• they exert a force and their momentum and direction change

• pressure created depends on speed and frequency

• increasing temperature increases pressure

• increasing volume decreases pressure

magnetic fields

region where magnetic materials experience a force

• magnetic field lines show size and direction of magnetic fields, always from north to south

  1. north to south

  2. at least 3 lines

  3. field lines closer at poles

magnetic materials

material that will turn into a magnet if it is brought into a magnetic field

1. iron

2. cobalt

3. nickel

magnetically hard

permanently magnetised, difficult to magnetise and demagnetise

• e.g. steel

magnetically soft

temporarily magnetised, easy to magnetise and demagnetise

• e.g. iron

uniform field

1. evenly spaced

2. parallel

3. arrow from north to south

magnetic induction

when a magnetic material is brought into a magnetic field, it becomes a magnet (gets magnetised)

• if brought to north pole, the side closest to the north pole will become the south pole

iron filings

1. place a white piece of paper over a bar magnet

2. sprinkle iron filings on top

3. gently tap the paper until magnetic field lines appear

compass

1. place multiple needle compasses around a bar magnet

2. needle of compass will align with the magnetic field

3. this will show the direction of the magnetic field

solenoid

when current flows through a current-carrying wire, it produces a magnetic field

1. magnetic field inside a current-carrying solenoid is uniform and strong

2. outside the bar, the field is one just like a magnet

3. ends of solenoid act as the north and south poles

fleming’s left hand rule

1. current flowing through a wire produces a magnetic field

2. this magnetic field interacts with the magnetic field of the permanent magnet

3. this produces a force

motor effect

loudspeakers

• current-carrying wire produces magnetic field

• A.C. current, meaning a current that changes direction continuously

• this magnetic field interacts with the magnetic field of a permanent magnet

• this produces a force -> every time the direction of the current changes, the direction of the force changes as well

• frequency of vibration correlates to the frequency of sound

factors that speed up a D.C. electric motor

1. more current

2. more turns in the coil

3. stronger magnetic field

4. soft iron core in the coil

electromagnetic induction

the creation of a voltage in a wire which is experiencing a change in magnetic field

• dynamo effect → using electromagnetic induction to generate electricity using energy from kinetic energy stores

  • to get a bigger voltage, increase

    1. strength of magnet

    2. number of turns on coil

    3. speed of movement

structure of an atom

• neutron number = mass - proton

• isotopes: same proton number but different number of neutrons

• proton

  • mass 1

  • charge +1

• neutron

  • mass 1

  • charge 0

• electron

  • mass 1/1000

  • charge -1

alpha radiation

• helium nucleus

• lowly penetrating

• highly ionising

• emitting an alpha particle causes proton number to decrease by 2, mass number decreases by 4

beta radiation

• electron

• moderately penetrating

• moderately ionising

• emitting a beta particle causes proton number to increase by 1, mass number stays the same

gamma radiation

• electromagnetic wave

• no mass, just energy

• highly penetrating

• lowly ionising

• always happens after an alpha or beta decay

• emitting gamma rays have no effect on the proton and mass number

neutron radiation

• emitting a neutron causes proton number to stay the same, mass number decrease by 1

measuring radioactivity of a sample

1. measure background radiation using a GM detector (Bq)

2. measure Bq reading from a known distance (control) to radioactive source

3. subtract background radiation reading from total Bq reading

4. repeat 3 times and average concordant results, remove anomalies

half-life

time taken for half of the radioactive nuclei to decay

nuclear fission

splitting of a large parent nucleus into smaller daughter nuclei and neutrons which collide with other nuclei, causing a chain reaction

nuclear fusion

two small nuclei collide and fuse to create a larger, heavier nucleus

• conditions → extremely high temperature (high kinetic energy) and pressure (to overcome electrostatic repulsion of like charges)

nuclear reactors

• moderator (usually graphite or water) slows down neutrons

• control rods (usually boron) limit rate of fission by absorbing excess neutrons

• shielding (usually thick concrete) used to absorb ionising radiation

• substance (usually CO2) pumped around to transfer energy to water in the heat exchanger

uses of nuclear radiation

1. medical tracers

   • radioactive source has to have a short half-life

2. sterilisation

   • of food and equipment

3. treating cancer

   • ionising radiation can kill or damage cells and tissues

4. industrial tracers and thickness gauges

risks of nuclear radiation

1. ionising radiation can damage cells and tissues

   • beta and gamma radiation can penetrate the skin and soft tissues

   • radiation collides with molecules in cells causing ionisation which damages or destroys molecules

2. irradiation

   • exposure to radiation

   • keeping sources in lead-lined boxes reduces risk of irradiation

3. contamination

   • radioactive particles getting onto objects

   • use gloves and tongs when handling sources

4. disposal

   • radioactive sources are difficult to dispose of

   • seal into glass blocks which are then sealed in metal canisters and buried underground

   • site must be geologically stable

universe

large collection of billions of galaxies

galaxy

large collection of stars

orbits

• planets orbit the sun

• comets orbit the sun

• asteroids orbit the sun

• moons orbit planets

elliptical orbit (elongated) → comets

circular orbit → planets

gravitational field strength affected by:

1. mass → higher mass higher g

2. distance → less distance higher g

orbital speed

2 x π x orbital radius/time period

stellar evolution

stars much bigger than the sun: nebula → protostar → main sequence star → red supergiant → supernova → neutron star or black hole

stars around the same size as the sun: nebula → protostar → main sequence star → red giant → white dwarf

star colour

(hottest) blue → white → yellow → orange → red (coolest)