Topic 1: Energy

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Xcxtherine

Cards (40)

energy is transferred between stores
when energy is transferred, energy is stored in an energy store
main ones are:
thermal energy store
kinetic energy store
gravitational potential energy store
elastic potential energy store
chemical energy store
magnetic energy store
magnetic energy store
electrostatic energy store
nuclear energy store
energy can be transferred mechanically, electrically, by heating or by radiation
system
single object or a group of objects you are interested in
when a system changes energy is transferred, into or away from the system between different objects or energy stores
closed systems - neither matter nor energy can enter or leave
the net change in the total energy if a closed system is always zero
work done
same as energy transferred
can be done when current flows or by a force moving
e.g. throwing a ball, car braking, car crash
falling objects
when a ball is dropped the gravitational force does work
energy from the gravitational energy store transfers to the kinetic energy store
when there's no air resistance
$energy\ lost\ from\ the\ g.p.e\ store\ =$ $energy\ gained\ in\ the\ kinetic$
air resistance causes some energy to be transferred to other energy store e.g. thermal
kinetic energy store
anything that moves uses the kinetic energy store
transferred to this store when an object speeds up and is transferred away when an object slows down
energy in the kinetic store depends on the mass and speed
the greater its mass and the faster it goes, the more energy it will have
formula $Ek=$ $\frac{1}{2}mv^2$
m- mass (kg)
v- speed (m/s)
energy is in joules (J)
Gravitational potential energy store
lifting an object in a gravitational field requires work
causes a transfer of energy to the g.p.e store
higher the object is lifted, the more energy is transferred to this store
amount of energy in the g.p.e depends on the mass, height and gravitational field strength
formula $Ep=$ $mgh$
m- mass (Kg)
g- gravitational field strength(N/Kg)
h- height (m)
elastic potential energy store
stretching or squashing an object transfers energy to the elastic potential energy store
as long as the limit of proportionality hasn't been exceeded
formula $Ee=$ $\ \frac{1}{2}Ke^2$
K- spring constant (N/m)
e- extension (m)
specific heat capacity
more energy needs to be transferred to the thermal energy store of some materials to increase their temperature than others
material that gain lots of energy in their thermal energy store to warm up transfer loads of energy when they cool down, can store a lot of energy
measure of how much energy a substance can store is called its specific heat capacity
definition - Specific heat capacity is the amount of energy needed to raise the temperature of 1Kg of a substance by $1^{\circ}C$
formula for specific heat capacity
formula $\Lambda E=$ $mc\Lambda\theta$
$\Lambda$ change in thermal energy (J)
m- mass (Kg)
c- specific heat capacity (J/K $g^{\circ}C$ )
$\Lambda\theta$ temperature change ( $^{\circ}C$ )
Specific heat capacity practical
To investigate a solid material you need a block of the material with two holes in it (for the heater and thermometer)
Measure the mass of the block, then wrap an insulating layer to reduce the energy transferred to the surroundings.
Insert the thermometer and heater
specific heat capacity experiment
Measure the initial temp of the block and set the potential difference, of the power supply to be 10V.
Turn on the power supply and start a Stopwatch
specific heat capacity
When power is turned on the current in the circuit does work on the heater, transferring energy electrically from the power supply to the heaters thermal energy store. This energy is then transferred to the material’s thermal energy store by heating, causing the materials temp to increase
Use the thermometer to measure its temp every minute. Keep an eye on the ammeter - the current through the circuit, shouldn’t change
can repeat with different material to compare specific heat capacities
Use the measurement of the current and the potential difference to calculate power supplied to the heater
P=VI
Use to find out how much energy has been transferred to the heater at the time reach temperature reading using e=Pt
Assume all the energy has been transferred to the block - you can plot a graph off energy transferred to. The thermal store of the block against temp
Find the gradient of the straight part (change in temp/change in energy)
Specific heat capacity of the material of the block is 1 divided (gradient x mass of the block)
conservation of energy principle
energy is always conserved
definition - energy can be transferred usefully, stored or dissipated, but can never be created or destroyed
when energy is transferred between stores, not all of the energy is transferred usefully - some is always dissipated
dissipated energy - “wasted” energy because energy is being stored in a way that is not useful (thermal)
power is rate of doing work
rate of energy transfer/work
power is measured in watts
1 watt=1 joule of energy transferred per second
equations p= e/t
P -power
E - energy
T- time
Powerful machine may not be one which exerts a strong force, but one that transfers a lot of energy in a short space of time
Conduction
Definition - conduction is the process where vibrating particles transfer energy to neighbouring particles
Energy transferred to an object by heating to the thermal store is also shared across the kinetic energy stores of the paticles
Particles being heated vibrate and collide more ,collisions cause energy to be transferred between particles‘ kinetic energy stores - conduction.
This continues throughout until the energy is transferred to the other side of the object - then it is transferred to the thermal store of the surroundings e.g. metal pan handle.
thermal conductivity
Thermal conductivity - measure of how quickly energy is transferred through a material in this way.
Higher the thermal conductivity the quicker the particles transfer energy
convection
convention is where energetic particles move away from hotter to cooler regions
can only happen in gases and liquids - renga transferred by heating
this energy is shared across the kinetic stores
particles are able to move, when you heat a region, the particles move faster and the space between particles increases - causes density of the region heated to be decreased
can flow, the war mer and less dense region will rise above denser,cooler regions
if there is a constant heat source, a convection current can be created
radiators
heating a room with a radiator relies on creating convection currents in the air
energy is being transferred from the radiator to the nearby air particles by conduction (particles collide with the radiator surface)
air becomes warmer and less dense (particles move quicker)
warm air rises and is replaced by cooler air - this air is then heated by the radiator
heated air transfers to the surroundings, cools becomes denser and sinks
this repeats an causes a flow of air to circulate around the room - convection current
lubrication
reduces frictional forces
when something moves, there is at least one frictional force against it
causes energy to be dissipated
air resistance transfers energy from a falling object‘s kinetic store to the thermal
lubrication: rubbed together
lubricants can be used to reduce friction
usually liquids so they can flow and coat objects easily
Insulation
Prevent energy losses
Have thick walls made from a material with a low thermal conductivity - thicker the walls and the lower their thermal conductivity, the slower the rate of energy transfer (building cools more slowly)
Thermal insulation
Cavity walls - inner and outer wall with an air gap in the middle. Gap reduces the amount of energy transferred by conduction.
Cavity wall insulation, gap filled by foam can reduce energy by convection
Loft insulation - often made of fibreglass wool, good insulator, reduces energy loss by conduction and prevents convection currents
Double-glazed windows - air gap between two sheets of glass, prevent energy transfer by conduction
Draught excluders - around doors and windows reduce energy transfers by convection
investigate the effectiveness of different insulators
boil water in a kettle. pour it into a sealable container
use a thermometer to measure the initial temp of the water
seal the container and leave it for five minutes, measure the time with a stopwatch
remove the lid and measure the final temperature of the water
pour away the water and allow the container to cool to room temperature
repeat this experiment but wrap the container in different material, use the same mass of water each time
temperature difference is reduced by wrapping the container in thermally insulating materials
factors affecting insulation
investigate thickness of the material affecting water temp
should find that the thicker the insulating layer, the less energy is transferred and the smaller the temperature change
efficiency
useful devices are useful because they transfer energy from one store to another
input energy usually wasted on a thermal energy store
less energy that is "wasted", the more efficient the device is
improve the efficiency of energy transfers by insulating objects, lubricating or making them more streamlined
use this equation $efficiency=$ $\frac{useful\ output\ energy\ transfer}{total\ input\ energy\ transfer}$
if you don't know energy inputs and outputs use $efficiency\ =$ $\ \frac{useful\ power\ output\ }{total\ power\ input}$
useful energy output $\ne$ total energy input
no device is 100% efficient
waste energy usually transferred to the thermal stores
electric heaters are exception - 100% efficient because all the energy in the electrostatic store is being transferred to the useful thermal store
all energy ends up transferred to thermal energy stores.
non-renewable energy resources
will run out
damage the environment
are reliable
are fossil fuels and nuclear fuel
fossil fuel - natural resources that form underground over millions of years
burnt to provide energy
three main are - coal, oi, natural gas
renewable energy resources
never run out
do damage but not as bad as non-renewables
don't provide much energy
some are unreliable because they depend on the weather
examples: solar, wind, waves, hydro-electricity, bio-fuel, tides and geothermal
energy resources used for transport
non-renewable: petrol diesel powered vehicles and coal for steam trains
renewable: electric cars and cars that use bio-fuels
energy resources for heating
non-renewable: natural gas in radiators, coal in fire places and electric heaters which generate electricity from non-renewable energy sources
renewable: geothermal heat pump, solar water heaters use the sun and burning bio-fuel or using electricity made from renewable energy sources
wind power
use of wind turbines in exposed places e.g. coast line
each turbines a generator - rotating blades turn the generator and produce electricity
no pollution - except manufacturing
do spoil the view - need 1500 turbines to replace one coal-fired power station, which is a lot of ground
wind power
very noisy for people living nearby
stops if the wind is too high or there isn't any - can't increase supply when there's extra demand
produce electricity 70-85% of the time
initial costs are high, no fuel costs and minimal running costs
no permanent damage to the landscape - remove the turbines, you remove the noise and the view returns
solar cells
generates electric currents directly from sun light
best source of energy to charge batteries in calculators and watches, don't use much electricity
used in remote places where there's not much choice and to power road signs and satellites
in sunny it is very reliable source of energy - only in the daytime
can be cost effective in cloudy countries
can't increase the power output when there is extra demand
no pollution - only in manufacturing
initial costs are high but the energies free and running costs almost nil
generate electricity on a relatively small scale
geothermal power
underground energy stores
only possible in volcanic areas where hot rocks lie quite near the surface.
energy is from the slow decay of various radioactive elements inside earth
free energy that is reliable with very few environmental problems
can be used to generate electricity or to heat buildings directly
not many suitable locations and the cost of building a power plant is high compared to the amount of energy it produces
hydro-electric power
transfers energy from the kinetic store of falling water
requires the flooding of a valley by building a big dam
rainwater is caught and allowed out through turbines
not really pollution
big impact on the environment due to the flooding of the valley - rotting vegetation releases methane and carbon dioxide and possible loss of habitat for some species
look very unsightly when dried up
putting them in remote valleys tends to reduce their impact on humans
hydro-electric power
can provide an immediate response to an increased demand for electricity
no problem with reliability unless in a drought
initial costs are high, no fuel costs and minimal running costs
generates electricity on a small scale in remote areas
wave power
lots of small wave-powered turbines around the coastline
turbines are connected to a generator
no pollution
main problems: disturbing the seabed, habitats of marine animals, spoiling the view and being a hazard to boats
fairly unreliable - waves die out when the wind drops
initial costs are high, no fuel costs and minimal running costs
never likely to provide energy on a large scale, can be very useful on small islands
tidal barrages
use the sun and moon's gravity
tidal barrages - big dams built across river estuaries with turbines
as the tide comes in it fill sup the estuary, the water is then allowed out through turbines at a controlled speed
tides are produced by the gravitational pull of the Sun and Moon
no pollution
tidal barrages
main problems: preventing free access by boats, spoiling the view and altering the habitat of the wildlife
pretty reliable happen twice a day without fail and always near to the predicted height. The height of the tide is variable so lower tides produces less energy than the bigger tides
doesn't work when the water level is the same either side of the barrage - four times a day
initial costs are moderately high, no fuel costs and minimal running costs
someone the most suitable estuaries have the potential for generating a significant amount of energy