Physics Paper 2

a push or pull that acts on an object due to the interaction with another object

friction, air resistance, tension, normal contact

gravitational force, electrostatic force, magnetic

force acting on an object due to gravity

- weight of an object acts at a single point
- can change (higher/lower) - lower gives more stability

directly proportional

calibrated spring balance (newton meter)

two components acting at right angles to each other - have the same effect as the single force

1 Joule

turning effect of it

- total clockwise moment about pivot = total anticlockwise moment about it
- resultant moment is zero

when applying a range of forces, allows a greater range of moments

- if the resultant force acting on an object is zero and the object is stationary, it remains stationary
- if the object is moving, it continues at the same speed and in the same direction

tendency of objects to continue in their state of rest / uniform motion

whenever 2 objects interact, they exert equal and opposite forces on each other

- small gear turns a large gear
- low speed because, with each turn of the small gear, the large doesn't turn as much
- high turning effect because distance from line of action is greater

- large gear turning small gear
- high speed because, with each turn of the large gear, the small turns several times
- low turning effect because distance from line of action is smaller

distance in a given direction

the force that makes an object move

shows the forces acting on an object without showing any other objects or forces

1.5 m/s

3 m/s

6 m/s

- 330 m/s but can vary
- speed of sound waves in air increases with temperature

rate of change of velocity

its speed at any particular time can be determined by drawing a tangent and measuring its gradient on a distance-time graph

acceleration

reached by an object when drag force is equal and opposite to the force making it move

- acceleration of an object is proportional to the resultant force acting on it
- and inversely proportional to the mass of the object

- how difficult it is to change the velocity of an object
- the ratio of force / acceleration

indicates an approximate value

brake overheating and loss of control

in a closed system, the total momentum before and after an event is the same

- increases impact time
- which reduces the rate of change of momentum per second
- which reduces the force of the impact
$F=\frac{\triangle momentum}{t}$

returns to its original shape when the forces deforming it are removed

- extension of an elastic object is directly proportional to the force applied, provided that the limit of proportionality is not exceeded
- so the work done on the spring and the elastic potential energy stored are equal

more than one force - there has to be an opposing force keeping one end / side stationary

- time taken to stop is longer - decelerating force reduced
- acts across chest so spreads force out

either a liquid or a gas

the pressure along the same horizontal level is constant

- air molecules colliding with a surface create atmospheric pressure
- number of air colecules (so weight of air) above a surface decreases as the height increases

- pressing cup onto wall squeezes any air trapped between cap and wall out
- atmospheric pressure only acts on outside of cap
- force due to atmospheric pressure keeps the cap on the wall

- air sucked out of straw
- atmospheric pressure acting on the liquid surface outside the straw pushes the liquid up

- a partially (or totally) submerged object experiences a greater pressure on the bottom surface than on the top surface
- this creates a resultant force upwards - upthrust
- when an object in a water container is fully immersed, volume of water displaced = volume of object
- the bigger the volume of water displaced, the greater the upthrust

- weight equal to upthrust
- density lower than water

- density greater than water - so weight of object is greater than weight of water displaced
- so weight is greater than upthrust

energy / info without transferring matter

- vibrations that travel through a medium (substance)
- sound, water, waves on springs and ropes, seismic waves caused by earthquakes
- can be transverse or longitudinal

no

- oscillations are perpendicular to the direction of energy transfer
- can move up and down or from side to side
- waves on a rope, water ripples, all EM waves

- oscillations are parallel to the direction of energy transfer
- show areas of compression and rarefaction
- sound waves

regions where the vibrating particles are closest together

regions where particles are furthest apart

- max displacement of a point on a wave away from its undisturbed position
- the bigger the amplitude, the more energy the waves carry

distance from a point on a wave to the equivalent position on the adjacent wave

number of waves passing a point each second

time for each wave to pass a fixed point

- aka straight waves
- waves all move at same speed and stay same distance apart

- distance travelled by a wave every second through a medium
- energy is transferred by the wave at this speed

repeatedly dipping the long edge of a ruler in water

- plane waves in a ripple tank are reflected from a straight barrier at the same angle to the barrier as the incident waves
- this is because their speed and wavelength don't change on reflection

- plane waves crossing a boundary between 2 different materials are refracted unless they cross the boundary at normal incidence
- refracted and incident waves have same frequency but travel at different speeds
- this means they have different wavelengths, so change direction
- can be observed in a ripple tank when water waves cross a boundary between deep and shallow

some or all of the wave may be reflected at the surface

- results in the substance gaining energy from the waves
- eg. when food is heated in a microwave, it absorbs the microwaves
- as waves travel through a substance, amplitude gradually decreases as the substance absorbs some of the waves' energy

- transmitted
- eg. light is mostly transmitted by normal glass but almost completely absorbed by darkened glass

sound waves make the eardrums vibrate in and out

- can't travel through
- can be tested by listening to an electric bell in a bell jar

sound waves reflect from smooth hard surfaces

- ripple tank for water waves
- stretched spring for waves in a solid
- signal generator and loudspeaker for sound waves

- 20 Hz - 20 kHz
- sound waves entering a solid are converted to vibrations - only works over a limited frequency range
- frequency doesn't change - when sound waves travel from one substance to another, only speed and wavelength can change
- intensity of sounds the ear can just about detect varies with frequency
- the cochlea is only stimulated by a limited range of frequencies
- the hairs in the human cochlea have different lengths and vibrate at different sound frequencies
- old age - shorter hairs that respond to higher frequencies stop working

solid - particles are more densely packed so vibrations travel faster

pulses of high frequency sound waves used to detect objects in deep water and measure depth below a ship

- transducer produces and detects pulses of ultrasound waves
- each wave is partially reflected from the different tissue boundaries in its path
- wave then returns to transducer as a sequence of waves reflected by the tissue boundaries, arriving back at different times
- this builds up an image on a screen of the internal tissue boundaries in the body

- scan organs and soft tissues
- waves don't have enough energy to remove electrons (ionise)

detect flaws or internal cracks in metal castings - internal crack creates a boundary inside the metal

waves that travel through the Earth

point where it originates from

nearest point on the surface to the focus

seismometers

- longitudinal - push and pull on material as they move through the earth
- cause initial tremors

- transverse - shake material that they pass through inside the earth from side to side
- slower than P-waves

- arrive last
- cause violent movement on the surface up and down, and backwards and forwards
- travel more slowly than p-waves and s-waves
- only happen in earth's crust

area on Earth's surface where no p-waves or s-waves are recorded

- p-waves are refracted at boundary between mantle and outer core when waves enter and leave
- this is due to speed changing abruptly at the boundary
- because the 2nd refraction is further around, the waves can't reach the shadow zone
- s-waves are transverse, so can't travel through liquid

weak p-waves detected in shadow zone show that there is a solid inner part that refracts p-waves at the boundary between inner and outer core into the shadow zone

speed of seismic waves changed at a certain depth below the surface

all types travel at the same velocity through a vacuum or air

- wavelength decreases after radio
- frequency (and energy) increases after radio

contains all the colours of visible light

- emitted by all objects
- the hotter an object, the more infrared it emits

can be absorbed by the skin - heats up skin cells - can damage, burn or kill

- optical fibres in communcations systems
- remote controls (send out a sequence of infrared pulses)
- infrared scanners in medicine (detect infrared emitted from hot spots on the body surface - can indicate that tissue underneath is unhealthy)
- infrared cameras
- electric heater and cookers (heat up objects quickly)

communication signals - can pass through atmosphere and reach satellites above Earth

- heat food faster than normal ovens
- microwaves penetrate food and are absorbed by water molecules in the food, heating it
- oven itself doesn't contain water molecules so doesn't become hot

instead of cables - connect electronic devices eg. bluetooth

penetrate people's bodies and can heat internal parts

used to carry any type of signal

- can carry more info (more pulses of wave)
- shorter range (due to increasing absorption by atmosphere)
- spread out less

send out radio signal when used - concerns about effects on health - more research needed

- very thin glass fibres used to transmit signals carried by light / infrared
- light rays can't escape - when they reach the surface of the fibre, they are reflected back into it (more secure)
- carry much more info than radiowaves due to short wavelength - can carry more pulses of wave

some chemicals emit light as a result of absorbing UV waves - posters and inks that glow in UV light

- harmful to eyes and can cause blindness (special goggles in sunbeds)
- in excess can cause sunburn and skin cancer

produced when electrons / other high speed particles are stopped - produced using x-ray tubes

detect internal cracks in metal objects - the more dense a substance is, the more x-rays it absorbs

- kill pathogens in food
- kill bacteria on surgical instruments
- narrow beam of gamma directed at a tumour

- pass through soft tissue but are absorbed by bones and teeth
- parts of the film / detector that the x-rays reach become darker - negative image of bones created
- organs consisting of soft tissue can be filled with a contrast medium that absorbs x-rays easily
- lead plates between tube and patient stop x-rays reaching other parts of the body
- longer wavelength and lower energy rays used - absorbed by bones but pass through gaps

- x-rays reach the cancerous tumour through a gap in the plates between the tube and the body
- shorter wavelength used - have enough energy to destroy the tumour

- when plane waves reflect from a flat barrier, reflected waves are at the same angle as the incident waves
- when each point on the wavefront reaches the barrier, it creates a wavelet moving away from the barrier
- this wavelet lines up with the previous reflected wavelets to form a reflected wavefront moving away from the barrier
- all parts of the wavefront move at same speed, so reflected wavefront at same angle to barrier as incident wavefront

reflection from a smooth surface - parallel light rays reflected in a single direction

from a rough surface - parallel light rays are scattered in different directions

refracted towards the normal

refracted away from the normal

waves that cross the boundary lose energy, so have a smaller amplitude than the incident waves - faint mirror image

filter absorbs all parts of the white light spectrum, apart from red

- depends on pigment chemicals and range of wavelengths in incident light
- pigments absorb light of specific wavelengths only and strongly reflect other wavelengths

transmit all the incident light that enters them

- let light pass through them, but it is scattered / refracted
- because material of object has lots of internal boundaries that change the direction of the light rays repeatedly

light is either scattered at surface, reflected, or absorbed - none is allowed to travel through

distance from centre of lens to principal focus

- an incident ray parallel to the axis refracts through the lens and passes through the principal focus on the other side
- an incident ray passing through the principal focus refracts through the lens and travels parallel to the axis
- incident ray passing through the centre of the lens carries on in same direction
- used in magnifying glasses and in cameras

- incident ray parallel to axis reracts through the lens and travels in line with principal focus (so it appears to have come from it)
- incident ray passing through the lens towards the principal focus refracts through the lens and travels parallel to the axis
- incident ray passing through centre of lens carries on in same direction
- used to correct short-sightedness

- convex lens - where rays hitting the lens parallel to axis all meet
- concave lens - where rays hitting lens parallel to axis appear to all come from

light from object comes together to form an image on a screen eg. retina

- rays are diverging, so the light from the object appears to be coming from a completely different place
- eg. mirror and magnifying lens
- can't be projected onto a screen

real or virtual

always virtual (always right way up, smaller than the object and on the same side of the lens as the object)

- convex lens used to produce a real image of an object on a film / array of pixels
- position of lens is adjusted to focus the image on the film
- distant object - distance from lens to the film must be equal to the focal length of the lens
- the nearer an object is to the lens, the bigger the distance from the lens to the film

iron, steel, cobalt, nickel

steel - doesn't lose its magnetism easily

- unmagnetised magnetic material is magnetised by placing in a magnetic field
- nearest poles of the induced material and the bar magnet always have opposite polarity
- so always a force of attraction

creates its own

series of concentric circles perpendicular to wire

long coil of insulated wire - used in devices where a strong magnetic field is needed

- increases in strength if current increases
- reverses its direction if current is reversed

- strong and uniform
- field lines are parallel to the axis of the solenoid and all in the same direction
- much stronger than if the wire was straight

like a bar magnet, except each field line is a complete loop because it passes through the inside

- solenoid in which the insulated wire is wrapped around an iron core
- magnetic field of the wire magnetises the iron bar
- when the current is switched off, the iron bar loses most of its magnetism

- switch in series with an electromagnet
- switch is held closed by a spring
- when current is too large, switch is pulled open by the electromagnet and stays open until it's reset manually

- when an electric bell is connected to a battery, the iron armature is pulled onto the electromagnet
- this opens the switch and the electromagnet is switched off
- because of this, the armature springs back and the switch closes again
- this is repeated in a cycle

- used to switch an electrical machine on / off
- small current used to magnetise iron core and pull armature onto electromagnet
- this closes the switch gap and switches the machine on

the stronger the field

- current carrying wire put between magnetic poles
- magnetic field around the wire interacts with magnetic field it has been placed in
- so the magnet and wire exert a force on each other - causes the wire to move
- a coil of current-carrying wire in a magnetic field tends to rotate - basis of an electric motor

- wire has to be at $90\degree$ to the magnetic field to experience the full force
- if wire runs parallel to the magnetic field, it won't experience any force at all
- direction of the force is always at right angles to the wire and the field lines
- direction of the force reversed if either the current or the magnetic field is reversed
- size of force can be increased by increasing current or using a stronger magnet

shows strength of magnetic field - how many field (flux) lines there are in a region (Tesla, T)

- current in one part of the rectangular coil causes a downward force
- current in the other part of the coil causes an upwards force
- these forces make the coil rotate
- when the coil is vertical, it moves parallel to the magnetic field, producing no force
- the momentum of the coil carries it on round a little
- split ring commutator changes the current direction every half turn, meaning each side of the coil is now near the opposite magnetic field

- swaps the positive and negative connections every half turn
- so direction of current through coil reverses every half turn
- this means forces acting on the coil will always be acting in the same direction
- this causes the coil to rotate continuously in one direction

cause very little friction when in contact with the rotating commutator

- creates a pd in a conductor and a current if the conductor is part of a complete circuit
- achieved by moving a magnet in a coil of wire or moving a conductor (wire) in a magnetic field (cutting the field lines)

- if you move the magnet / conductor in the opposite direction / reverse the polarity of the magnet, the pd / current will be reversed
- if you keep the magnet / coil moving backwards and forwards, you produce a pd that keeps swapping direction - AC

- as a magnet turns, the magnetic field through the coil changes
- this change in magnetic field induces a pd, which can made a current flow
- once the magnet has been turned through half a turn, the direction of the magnetic field reverses the pd, making the current flow in the opposite direction
- if the magnet keeps turning in the same direction, the pd will keep reversing every half turn - AC

a changing magnetic field

opposes it - second magnetic field is created around the wire

- increase the rate at which the magnetic field is changing:
- increase strength of magnetic field (so there are more field lines that can be cut)
- increase speed of the movement (to cut more field lines in a given time)

- rectangular coil is forced to spin in a uniform magnetic field
- coil is connected to a centre-reading meter by metal brushes that press on 2 metal slip rings
- slip rings and brushes provide a continuous connection between the coil and the meter
- when the coil turns steadily in one direction, the current in the circuit repeatedly changes direction

when plane of coil is parallel to the direction of the magnetic field - sides of coil cross directly through the magnetic field lines so induced pd is at peak value

- when plane of coil is perpendicular to the magnetic field lines
- sides of the coil move parallel to the field lines and don't cross them

make the coil rotate faster - each full cycle of the alternating pd takes the same time as one full rotation of the coil

- make the coil rotate faster - sides of the coil cross through the magnetic field lines at a faster rate
- use a magnet with a stronger magnetic field
- use a coil with a bigger area and more turns of wire on it

- same as alternators but have split-ring commutators instead of slip rings
- this swaps the connection every half turn to keep the current flowing in the same direction

- show how pd generated in a coil changes over time
- height of the line = pd
- increasing frequency of revolutions increases overall pd but also creates more peaks

- work by the generator effect
- soundwaves hit a flexible diaphragm that is attached to a coil of wire wrapped around a magnet
- this makes the coil of wire move in the magnetic field, which generates current
- movement of the coil depends on the properties of the soudwave (loud sounds make the diaphragm move further)
- pressure variations in the soundwave are converted into variations in current in an electric current

- work by motor effect
- AC sent through a coil of wire attached to the base of a paper cone
- coil is surrounded by one pole of a permanent magnet and surround the other pole
- the current causes a force on the coil, making the coil move
- when the current reverses, the force acts in the opposite direction, making the cone move in the opposite direction as well
- variation in the current make the cone vibrate, making the air around the cone vibrate
- this creates variations in pressure and produces a sound wave

frequency of the AC

- alternating pd applied across primary coil, so the iron core magnetises and demagnetises quickly
- this changing magnetic field induces an alternating pd in the secondary coil
- if the secondary coil is part of a circuit, a current is induced

equal to ratio between their number of turns

more turns on secondary coil

easily magnetised and demagnetised

full efficiency assumed in GCSE calculations

- nebula (cloud of dust and gas) particles are pulled together by their own gravitational attraction
- this makes particles speed up
- clouds merge together and become more and more concentrated to form a protostar

- protostar becomes denser - particles speed up and collide more
- temperature increases - process transfers energy from the protostar's gravitational potential store to its thermal store
- when temperature gets high enough, hydrogen nuclei undergo fusion to form helium nuclei
- this gives out lots of energy, keeping the core hot

objects too small to be stars can be attracted by a protostar to become planets orbiting the star

- energy released in core keeps it hot, so fusion continues
- radiation (eg. gamma) flows out steadily from the core in all directions

- gravity acts inwards, trying to make the star contract
- force of radiation from nuclear fusion in the core acts outwards, trying to make the star expand
- these forces stay in equilibrium until most of the hydrogen nuclei in the core have been fused together

core collapses

- swell out, cool down and turn red - red giants
- helium and other light elements in the core fuse to form heavier elements
- when there are no more light elements in the core, fusion stops and no more radiation is released
- star collapses in on itself due to its own gravity
- heats up as it collapses and turns into a white dwarf
- white dwarf fades out, goes cold and becomes a black dwarf

- swell out to red supergiants, then collapse
- in the collapse, the matter surrounding the core compresses the core more and more
- compression suddenly reverses in a supernova explosion - can outshine an entire galaxy for several weeks
- explosion compresses the core into a neutron star - extremely dense object only made up of neutrons
- if the star is big enough, it becomes a black hole - gravitational field so strong that nothing can escape from it

increase across the spectrum from blue to red

- light waves are stretched out and wavelengths are increased
- makes the spectrum of light switch towards the red part of the spectrum - red shift

- light waves are squashed together and wavelengths are reduced
- this makes the spectrum of light shift towards the blue part of the spectrum - blue shift

- dark spectral lines are caused by absorption of light by specific atoms such as hydrogen
- position of these lines shows if there is a shift and what type of shift it is

the bigger the shift - so the more squashed together / stretched out the waves are

- light from distant galaxies is red-shifted
- the further a galaxy is from the Earth, the bigger its red-shift

- distant galaxies are receding from Earth
- the greater the distance of a galaxy from Earth, the greater the speed at which it is moving away
- so the universe is expanding

- formed from fusion in stars - hydrogen nuclei fused into helium and other small nuclei
- red giants fuse helium and other small nuclei into larger nuclei
- nuclei larger than iron can't be formed in this way - too much energy needed

- formed when a massive star collapses and then explodes as a supernova
- enormous force of collapse fuses small nuclei into nuclei larger than iron
- explosion scatters elements throughout universe
- debris contains all known elements - new stars and planets form from this

- force of gravity on a planet from the sun acts towards the centre of the sun
- thsi is the resultant force on the planet because no other forces act on it

- centripetal force would cause the planet to just fall towards the sun, but as the planet is already moving, it just changes direction
- planet moves in a circle so has a constantly changing velocity
- so constantly accelerating (acceleration = change in v per second)
- force on the planet is at right angles to its direction of motion
- so no work is done on the planet - kinetic energy and speed don't change
- planet keeps accelerating towards the sun but instantaneous velocity keeps it travelling in a circle

the curved path of one celestial object or spacecraft around another

- the stronger the gravitational force
- so satellites need to move faster to stay in orbit
- shorter amount of time to move around the orbit once (circumference is smaller and speed is greater)

a small body must move at a particular speed around a larger body

- gradually lose speed due to atmospheric drag when satellite's orbit is in the upper atmosphere
- if a satellite loses speed, it gradually spirals inwards until it hits the Earth's surface

- they orbit the Earth in the same direction as the Earth's spin, with a period of 24 hours
- communications satellites

- much lower orbits than geostationary - once every 2 /3 hours
- weather forecasting and environment monitoring

- universe is expanding after exploding suddenly from a very small and extremely hot and dense region
- space, time and matter were created in the Big Bang

galaxies are being pushed apart by matter entering the universe through 'white holes' - opposite of black holes

- if the universe started with the Big Bang, then high-energy radiation must have been produced shortly after
- this would have stretched as the universe expanded and become lower-energy radiation
- cosmic microwave background radiation (CMBR) discovered coming from every direction in space
- this used to be gamma but wavelengths got longer until it was microwaves

- astronomers think that the stars in a galaxy account for only a small percentage of its total mass
- galaxies would spin much faster if their stars were the only matter
- missing mass = dark matter

dark matter means that the average density of the universe is much bigger than if it didn't exist

if the density of the universe is less than a particular amount, it will expand forever and stars will die out

if the density of the universe is more than a particular amount, it will stop expanding and go into reverse

- distant galaxies are accelerating
- gravity is the only known force on the distant galaxies but can't be used to explain dark energy because it's an attractive force

- object that absorbs all the radiation that hits it - none is reflected or transmitted
- since a good absorber is also a good emitter, a perfect black body would be the best possible emitter

- all objects emit EM radiation due to the energy in their thermal stores
- this is not just infrared - covers a range of wavelengths and frequencies

- intensity and distribution of wavelengths emitted by an object depend on its temperature
- intensity is the power per unit area - how much energy is transferred to a given area in a given amount of time
- as the temperature of an object increases, the intensity of every emitted wavelength increases
- intensity increases more rapidly for shorter wavelengths
- this causes the peak wavelength (with the highest intensity) to decrease / be of a shorter wavelength

- in the day, lots of radiation (like light) is transferred to Earth from the Sun and absorbed - increase in local temperature
- at night, less radiation is being absorbed than is being emitted, which decreases the local temperature
- overall Earth temperature remains fairly constant
- if atmosphere starts to absorb more radiation without emitting the same amount, the overall temperature will rise until absorption and emission are equal again