Physics Paper 1

amount of energy needed to raise the temp of 1kg of a substance by 1*C

chemical

cold spoon dropped into an insulated flask of hot liquid

process where vibrating particles transfer energy to neighbouring particles

- where energetic particles move away from hotter regions to cooler regions
- only occurs in liquids and gases

- when a region of a gas / liquid is heated, the particles move faster
- space between particles decreases - so density decreases
- because liquids and gases can flow, the warmer and less dense region will rise above the denser, cooler regions
- if there is a constant heat source, a convection current can be created

- energy transferred when air particles collide with radiator surface
- air by the radiator becomes warmer and less dense
- warm air rises and is replaced by cooler air

copper

Glass

electric heaters

temp increases more slowly when object with greater mass is heated

used in loft insulation - air between fibres reduces rate of energy transfer by conduction

insulation pumped into cavity, better insulator than air it replaces, traps air in small pockets - reducing rate of energy transfer by conduction

reflects radiation away from wall - reducing rate of energy transfer by radiation

two glass panes with dry air/vacuum inbetween. Dry air reduces rate of energy transfer by conduction, vacuum reduces rate by convection

reduce energy transfers by convection

emits infrared at the same rate as it absorbs it and emits across a continuous range of wavelengths

• Uranium fuel in sealed cans at core of reactor
• Unstable nuclei split in 2, transferring energy
• Core becomes very hot from many uranium atoms undergoing fission
• Energy of core transferred by the coolant fluid that is pumped through it
• Newly hot coolant fluid leaves core and flows through pipe to heat exchanger, then back to reactor core
• Energy transferred turns water into steam in the heat exchanger

• Motion of waves makes floating generator move up and down, generating electricity
• Cable between generator and shoreline delivers electricity to grid system

• Water from high tide is trapped behind a barrage
• Then released back into sea through turbines

- flooding of the valley makes vegetation rot (releases methane and CO2)
- loss of habitat

- take up space / water needed for food crops
- forest clearing - loss of habitat and decay and rotting of vegetation increases methane and CO2

use solar energy to generate electricity directly

• Convert very little of the solar energy they absorb - only useful where small amounts of electricity are needed (e.g., watch)
• Expensive to buy

• Cost nothing to run
• Can be connected to make solar cell panels

heat water that runs through them

• Thousands of flat mirrors reflect sunlight on to a big water tank at the top of a tower
• Mirrors on the ground surround base of tower
• Water in tank turned into steam by heating effects of solar radiation directed at it
• Steam piped down to ground level
• Mirrors are controlled by a computer to track the sun

• Energy transferred from radioactive substances deep within the Earth heats surrounding rock
• Water is pumped down to these rocks to produce steam

• Heat flow from underground can heat buildings in some areas geothermally and directly
• Heat flow heats water in long underground pipes – then pumped up to buildings

- not many suitable locations
- cost of building often high compared to amount of energy produced

sulfur can be removed from fuels before burning

Carbon capture and storage - expensive

much more energy transferred from each kg of uranium/plutonium fuel than fossil fuels

• Fuel rods contain radioactive waste
• Expensive to build, run and decommission

can't start up instantly - depends on type of power

cheap to run but expensive to install

• Nuclear and coal provide the base load demand (constant amount of electricity)
• Gas and pumped storage schemes meet daily variations in demand and extra demand in winter
• Renewable used when demand is high, and conditions are suitable
• Renewable produced when demand is low – stored in pumped-storage schemes

the flow of electrical charge

light emitting diode - emits light when a current passes through it

allows current to be varied

resistance decreases as temp increases

resistance decreases as light intensity increases

- circuit with a thermistor and a loop made up of a fixed resistor and fan in parallel
- pd of the power supply is shared out between them according to their resistances
- the bigger a component's resistance, the more of the pd it takes
- as the room gets hotter, the resistance of the thermistor decreases and it takes a smaller share of the pd from the power supply
- so the pd across the fixed resistor and the fan rises, making the fan go faster

- bulb connected in parallel to an LDR
- pd across both will be high when it's dark because the LDR's resistance is high
- the greater the pd across the component, the more energy it gets
- so the bulb gets brighter as the room gets darker

same everywhere

• Current through an ohmic conductor at a constant temp is directly proportional to the pd across it
• Means the resistance remains constant as the current changes

yes

lamps, diodes, thermistors, LDRs

increases as temp of filament increases

very high in the reverse direction

temp sensors in fire alarms, ovens, digital thermometers

light sensors - automatic lights in the dark, light intensity meters

shared between components

sum of currents through each component

same everywhere

less than resistance of smallest individual resistor

• Total pd shared between more resistors so pd across each is less than before
• Current through the resistors is therefore less than before
• As the total pd is unchanged and the current goes down, resistance increases

more pathways for the current to go through - so easier to flow through the circuit

stops appliance being damaged if batteries are put in wrong way round

measure of energy transferred to a component by each coulomb of charge that passes through it

polythene and acetate rods being rubbed with a cloth duster

- happens when there is a high enough pd between a charged object and the earth (or an earthed object)
- strong electric field between the charged object and the earthed object
- causes electrons in the air particles to be removed (ionisation)
- air is normally an insulator but, when ionised, is much more conductive, so a current can flow through it

- electrons can jump to any earthed conductor nearby if the pd is large enough
- charge builds up on the car's metal frame
- when the car is touched, the charge travels through the body to the earth

AC, 50 Hz, 230 V

copper

by making the potential difference very large, much less current is needed to transfer the same amount of power

brown, carries alternating pd from supply

blue, completes circuit

green and yellow, stops appliance casing becoming live

close to/at 0V

- a large pd is produced across your body and current flows through you
- even if the switch is off, still dangerous - no current flowing but still a pd in the live wire - your body would provide a link between the supply and the earth, so a current would flow through you

complete circuit from mains supply to ground is made - shock or fire likely

connected to earth wire - appliances with metal cases have their cases automatically earthed when plugged in

brass - good conductor, doesn't rust or oxidise

between the live pin and live wire

appliances with plastic cases

thicker than those that join together light fittings - more current passes along so they have to be thicker to have less resistance heating

- live wire inside an appliance touches neutral wire - very big current passes between the two
- provided fuse blows, current is cut off

less energy loss as cables are shorter

- cables are cooled by air (no cooling systems needed)
- air acts as an insulator (no layers of insulation needed)

potential repeatedly changes from + to - and back every cycle

total kinetic + total potential

the internal energy (not the temperature)

- amount of energy needed to change the state of 1kg of a substance with no change in temperature
- for cooling - energy released by a change in state

a net force at right angles to the walls of a gas container

total force exerted by all of the particles in the gas on a unit of area of the container walls

can increase - work is done on the gas and this energy isn't transferred quickly enough to the surroundings

occupies the greatest volume but mass in each state is the same

- pressure of a gas causes a net outwards force at right angles to the surface of its container
- also a force on the outside of the container due to the pressure of the gas around it
- if a container can easily change its size (eg. balloon), then any change in these pressures will cause the container to compress or expand, due to the overall force

- atmospheric pressure decreases with altitude so the pressure outside the balloon decreases
- this makes the balloon expand until the pressure inside drops to the same as the atmospheric pressure

strong - keep particles in place and only vibrating about fixed positions

particles have enough energy to break free from some forces of attraction

none

individual motions of partices relative to each other

individual positions of partices relative to each other

gravitational potential energy or kinetic energy caused by motion of the whole substance

absorption of EM radiation can make electrons move further away from the nucleus to a high energy level

- noticed that light emitted by substances on heating had very specific amounts of energy
- this was the energy emitted as electrons fell to a lower energy level

random process of unstable nuclei giving out radiation as they change to become more stable

rate at which a source of unstable nuclei decays, Bq

number of decays recorded each second by a detector

from the nucleus as a neutron turns into a proton

neutrons (n)

thin sheet of paper

about 5cm

- ionises air particles, causing a current to flow
- if there is smoke in the air, it binds to the ions
- so the current stops and the alarm sounds

- 5mm aluminium sheet
- 2-3mm lead sheet

about 1m

test thicknesses of sheets of metal

- several cm lead sheet
- over 1m concrete

way of getting rid of excess energy from a nucleus

time for number of nuclei of the isotope or count rate to halve

activity never quite reaches zero

unwanted presence of materials containing radioactive atoms on other materials

Sieverts (Sv)

due to high doses that kill lots of cells completely - vomiting, tiredness and hair loss

- absorbed by thyroid gland (like normal iodine-127)
- gives out radiation that can be detected to indicate whether thyroid gland is taking in iodine as it should

initial count rate $/$ 2$n$

rocks and cosmic rays

- contain a radioactive isotope that emits gamma
- patient drinks water containing a tiny amount of the radioactive substance

rare - usually a neutron must be absorbed

- nucleus splits into 2 smaller daughter nuclei (roughly equal in size) and emits 2-3 neutrons plus gamma rays
- these neutrons can start a chain reaction
- all fission products have kinetic energy
- energy not transferred to kinetic energy stores of products is carried away by gamma rays

control rods lowered and raised inside nuclear reactor to absorb neutrons, slow down chain reaction and control amount of energy released

- two light nuclei collide at a high speed and fuse to create a larger, heavier nucleus
- heavy nucleus doesn't have as much mass as the 2 separate nuclei
- some of the mass is converted to energy