P1 Flashcards
examples of energy stores?
thermal KE GPE EPE Chemical Magnetic Electrostatic Nuclear
how is energy transferred mechanically
by a force doing work
how is energy transferred electrically
by moving charges
ions/delocalised electrons
how is energy transferred by heating/radiation
by light or sound
what’s a system
an object or group of objects
what happens when the system changes
energy is transferred into or away from the system, between different objects or different types of energy stores
what’s a closed system
system where matter or energy can’t leave
net change of total energy is always 0
explain the energy transfer by heating in a kettle
energy is transferred to water (from kettle heating agent) by heating into the thermal energy store
temp. increases
define work done
another way of saying energy transferred
how can work be done
when a current flows
or by a force moving an object
explain how work is done when a ball is thrown upwards
initial force exerted by person to throw ball up does work
energy transfer from chemical energy store to KE energy store of the ball and arm
explain how work is done when a ball is dropped from a height
ball dropped from a height is accelerated by gravity- the force does work
causes energy ti transfer from ball’s GPE to KE store
explain how work is done when an object slows down (car)
friction between car’s brakes and its wheels does work as it slows down
energy transfer from wheels’ KE store to thermal store of surroundings
explain how work is done when a moving object (car) hits an obstacle/stationary object
when they collide, normal contact force does work
energy transfers from car’s KE tore to other stores e.g. elastic/thermal of obstacle and car body
some energy transferred as sound waves
what’s the KE equation?
KE = ½ x m x v²
(mass in kg)
(energy in J)
(speed in (m/s)²)
what’s the GPE equation?
GPE = m x g x h (energy in J) (mass in kg) (GFS in N/kg) (height in metres)
what’s the rule when there’s a falling object with no air resistance?
energy lost from GPE store = energy gained in KE store
what’s the EPE equation?
EPE = ½ x k x e²
(energy in J)
(spring constant in N/m)
(extension in metres)
what’s SHC
amount of energy needed to raise the temp. of 1kg of a substance by 1°C
what’s the SHC equation?
ΔE = m x c x ΔT (energy in J) (mass in kg) (SHC in J/kg°C) (temp. in °C)
explain SHC practical
1) get a block of a material (copper)
2) put 2 holes in it for heater and thermometer
3) measure block mass
4) wrap block in insulation layer to reduce energy transfer to surroundings
5) insert thermometer and heater
6) measure initial temp of block
7) set p.d. to 10V, turn on power supply and stop watch
8) current in circuit does work on heater, so energy electrically transferred from from power supply to heater’s thermal store by heating so temp increases
9) take readings every min for 10 mins, current doesnt change
10) after 10 readings calc power supplied and energy transfer to heater
define the term power
the rate at which energy is transferred/work is done
which equation links power and energy/work done?
power (Watts) = energy transferred OR work done (J)
——————————————————
time (secs)
how many Watts is 1 Joule per second?
1 Watt
what equation links power, current and voltage
Power = Current x Voltage
what’s the conservation of energy rule?
energy can be transferred usefully, stored or dissipated, but can never be created or destroyed
what happens to waste energy
it’s dissipated so it’s stored in less useful ways
how can unwanted energy transfers be reduced?
lubrication to reduce friction->liquids/oils
insulation to reduce transfer by heating->thermal insulation (double-glazed windows)
how is energy dissipated in a mobile phone?
energy is transferred from chemical store in battery
but some energy is dissipated during the transfer to the thermal store of the phone, so its temp. increases
how is energy dissipated in a closed system e.g. spoon in soup?
cold spoon dropped into sealed insulated flask of hot soup
flask is a perfect thermal insulator so a closed system is formed
energy transferred from thermal store of soup to useless thermal store of spoon, soup cools down
energy transfer occurred but none left the system so net energy change is 0
what can a powerful machine do? (a machine with high power)
transfer a lot of energy in a short amount of time
power = energy / time
what’s the link between thermal conductivity and energy transfer?
the higher the thermal conductivity of a material the higher the rate of
energy transfer by conduction across the material
how do walls affect the cooling of a building?
thick walls made of low thermal conductivity material
the thicker the walls and the lower their thermal conductivity, the slower the rate of energy transfer -> cools slower
what’s conduction
process by which vibrating particles transfer energy to neighbouring particles (ONLY SOLIDS)
what’s convection
where energetic particles move away from hotter to cooler regions (ONLY LIQUIDS AND GASES)
what’s a convection current
warmer/less dense region rises over cooler/more dense regions
if there’s a constant heat source it rpeats
how do radiators create convection currents?
1) energy transferred from radiator to nearby air particles by conduction
2) air near radiator gets warmer/less dense and moves quicker (more KE)
3) warm air rises and is replaced by cooler air
4) cooler air is heated
5) previously heated air transfers energy to surroundings, cools/becomes less dense and sinks
6) cycle repeats
PAG: investigate effectiveness of different materials as thermal insulators
1) boil water in kettle and pour some into sealable container at a safe level
2) measure volume of water in container
3) use thermometer to measure initial temp
4) seal and leave for 5 mins with stopwatch
5) measure final temp. pour away water, let container cool to room temp.
6) repeat with same water volume with different materials with different thickness
7) the lower the temp. difference, the better the thermal insulator
what’s the efficiency equation?
efficiency = useful output / total input
why is useful energy input not always equal to total energy output?
no device is 100% efficient
energy can be dissipated as waste
define a renewable energy resource
a resource that’s being (or can be) replenished
as it’s being used
non-renewable energy sources
fossil fuels (coal, oil, natural gas) nuclear fuel
examples of renewable sources
solar wind hydro-electric bio-fuel tides geothermal water waves
what are the main energy resources available for use on Earth?
fossil fuels (coal, oil and gas) nuclear fuel biofuel wind hydro-electricity geothermal tides the sun water waves
state some uses of energy resources
transport
electricity
generation
heating
