Studied by 148 people
Energy Stores
Elastic potential
Gravitational potential
Thermal
Electrostatic
Nuclear
Chemical
Kinetic
Magnetic
Light
Sound
How is energy transferred?
Mechanically - force doing work
Electrically - work done by moving charges
Heating/Radiation - light, sound
How can work be done?
When a current flows or by a force moving an object
Kinetic energy formula
E=1/2mv² Kinetic energy(J) = 0.5 x mass(kg) x speed²(m/s)
Gravitational potential energy formula
E=mgh G.P.E(J) = mass(kg) x gravitational field strength (N/kg) x height (m)
What happens when an object falls and there's no air resistance?
Energy lost from the g.p.e store = energy gained in the kinetic energy store
What does air resistance do when acting against falling objects?
It causes some energy to be transferred to other energy stores e.g. the thermal energy stores of the object and the surroundings
Elastic potential energy formula
E=1/2ke² E.P.E(J) = 0.5 x spring constant(N/m) x extension²(m)
What is SHC?
The amount of energy needed to raise the temperature of 1kg of a substance by 1°C
SHC formula
E=mcθ Change in thermal energy(J) = mass(kg) x SHC(J/kg/°C) x temperature change(°C)
What is the conservation of energy principle?
Energy can be transferred usefully, or stored or dissipated (wasted energy), but can never be created or destroyed
What is power?
The rate of energy transfer, or the rate of doing work
What is 1W equal to?
1J of energy transferred per second
Power Equation 1
E=Pt Energy transferred(J) = power(W) x time(s)
Power Equation 2
W=Pt Work done(J) = power(W) x time(s)
What is conduction?
The process where vibrating particles transfer energy to neighbouring particles Energy is transferred to thermal stores of the object - this energy is shared across the kinetic energy stores
What is thermal conductivity?
A measure of how quickly energy is transferred through a material via conduction
What is convection?
Where energetic particles move away from hotter to cooler regions Energy is transferred to the thermal energy stores of the object and is shared across the kinetic stores
What do radiators create?
Convection currents
Convection currents - process
Energy is transferred from the radiator to the nearby air particles by conduction
The air by the radiator becomes warmer and less dense as the particles move quicker
The warm air rises and displaces the cooler air, which is then heated by the radiator
The previously heated air transfers energy to the surroundings - the air cools, becomes denser and sinks
What does lubrication do?
Reduce frictional forces
What does insulation do?
Reduce the rate of energy transfer by heating
Thermal insulation techniques
Cavity walls - made up of an inner and outer wall with an air gap in the middle - the air gap reduces the amount of energy transferred by conduction through the walls
Cavity wall insulators - the air gap is filled with foam also reduces energy transfer by convection in the wall cavity
Loft insulation - reduces convection currents being created in lofts
Double-glazed windows - air gap between two sheets of glass that prevent energy transfer by conduction through the windows
Draught excluders - reduce energy transfers by convection around doors and windows
How do you improve efficiency?
Lubrication
Insulation
Making objects more streamlined
Efficiency - energy transfer equation
Useful output energy transfer divided by total input energy transfer
Efficiency - power equation
Useful power output divided by total power input
Is any device 100% efficienct?
No
Where is wasted energy usually transferred?
Thermal energy stores
How do thick walls prevent energy losses through heating?
They're made from a material with a low thermal conductivity - the thicker the walls, the lower the thermal conductivity, the slower the rate of energy transfer
What objects are usually 100% efficient?
Electric heaters - all the energy in the electrostatic energy stores is transferred to useful thermal energy stores
Fossil fuels (coal, oil, natural gas)
Non-renewable Cause acid rain Cause global warming Reliable currently - they are finite, so they will run out eventually Coal mining ruins the landscape Oil spillages cause serious environmental problems
Energy resources used for transport
Petrol and diesel from oil - non-renewable Coal (steam trains) - non-renewable Bio-fuels - renewable
Energy resources used for heating
Natural gas - non-renewable Coal - non-renewable Electric heaters - non-renewable Geothermal - renewable Solar water heaters - renewable Bio-fuels - renewable
Wind Power
Renewable Doesn't cause global warming Doesn't cause acid rain No pollution No permanent damage to the landscape Free - initial costs are high Very noisy Spoil the view Not always reliable
Solar Power
Renewable Doesn't cause acid rain Doesn't cause global warming No pollution Free - solar panels are expensive though Not always reliable
Geothermal Power
Renewable Doesn't cause acid rain Doesn't cause global warming Free Very little damage to the environment Not very reliable - can only happen in certain places and there aren't very many of them
Hydroelectric Power
Renewable Reliable Doesn't cause acid rain Doesn't cause global warming No pollution Provides an immediate response to high demand Free - initial cost is high Big impact on environment and possible loss of habitat
Wave Power
Renewable Doesn't cause acid rain Doesn't cause global warming Free - initial costs are high Not always reliable - waves die out when the wind drops Disturbs the seabed and habitats of marine wildlife Spoils the view Hazard to boats
Tidal Power
Renewable Reliable Doesn't cause acid rain Doesn't cause global warming No pollution Free - initial costs are moderately high Spoils the view Alters the habitats of wildlife
Bio-fuels
Renewable Reliable Doesn't cause acid rain Carbon neutral Free Can cause global warming Loss of natural habitat from destruction of forests Cannot respond to immediate energy demands
Nuclear Power (Uranium or Plutonium)
Doesn't cause acid rain Doesn't cause global warming Reliable currently - finite Non-renewable High decommissioning costs Produces radioactive waste - no other pollution Nuclear waste is dangerous and hard to dispose of
Investigating Specific Heat Capacities - Method
Measure the mass of a block with two holes in it, then wrap it in an insulating layer (e.g. newspaper) to reduce the energy transferred from the block to the surroundings. Insert the thermometer into one hole and the heater into another
Measure the initial temperature of the block & set the potential difference of the power supply to be 10V. Turn on the power supply & start a stopwatch
When you turn on the power, the current in the circuit does work on the heater, transferring energy electrically from the power supply to the heater's thermal energy stores - this energy is then transferred to the material's thermal energy store by heating, causing its temperature to increase
As the block heats up, take readings of the temperature and current every minute for 10 minutes - the current shouldn't change
Turn off the power supply. Use the measurements of the current & the p.d. to calculate the power supplied to the heater, thus calculating how much energy has been transferred to the heater at the time of each temperature reading
If you assume all the energy supplied to the heater has been transferred to the block, you can plot a graph of energy transferred to the thermal energy store of the block against temperature
Investigating the Effectiveness of Materials as Thermal Insulators - Method
Boil water in a kettle. Pour some of the water into a sealable container to a safe level. Measure the mass of water in the container
Use a thermometer to measure the initial temperature of the water
Seal the container & leave it for 5 minutes. Measure this time using a stopwatch
Remove the lid & measure the final temperature of the water
Pour away the water & allow the container to cool to room temperature
Repeat this experiment, but wrap the container in a different material once it has been sealed. Ensure the mass of water is the same and so is the initial temperature each time
What is a closed system?
A system where neither matter nor energy can enter or leave
Why did electricity use in the 20th century increase?
The population grew
People began to use electricity for more & more things
Why did electricity use in the 21st century decrease?
Appliances are becoming more efficient
We're more careful with energy use in our homes
Why are we trying to increase our use of renewable energy resources?
Burning fossil fuels is damaging to the environment
Non-renewables will run out one day
Pressure from other countries & the public has led to targets being set e.g the UK aims to use renewable resources to provide 15% of the total yearly energy by 2020
What has pressure from the public & other countries led to?
Pressure being put on energy providers to build new power plants that use renewable resources to ensure that they don't lose business & money
What is the use of renewables limited by?
Reliability - since some energy resources aren't that reliable, a combination of different power plants would have to be used - expensive
Money - building new power plants costs money, the cost of switching to renewable power will have to be paid & some people don't want to or can't afford to pay
Politics - companies and governments can't force people to change their behaviour
What happens when a system changes?
Energy is transferred - it can be transferred into/away from the system, between different objects in the system or between different types of energy stores
Why are wind turbines unlikely to be able to power everything in the UK?
Large numbers of turbines would need to be built - takes up space & is expensive
Not always windy - the same amount of electrical power won't be produced every day
What is electric current?
The flow of electrical charge
What is electric current measured in?
Amps
What is potential difference?
Voltage - it pushes the electric charge around the circuit
What is potential difference measured in?
Volts
What is resistance?
Anything that slows the flow down
What is resistance measured in?
Ohms
The greater the resistance...
...the smaller the current that flows
What is the formula for charge?
Charge (coulombs) = current (amps) x time (seconds) Q=It
What is the formula for voltage?
Potential difference (volts) = Current (amps) x Resistance (ohms) V=IR
The longer the wire...
...the greater the resistance
Is the ammeter placed in series or parallel?
Series
Is the voltmeter placed in series or parallel?
Parallel
Do Ohmic Conductors have a constant resistance?
Yes - at a constant temperature, the current is directly proportional to the potential difference
What does resistance change in?
Diodes and filament lamps
Why does resistance increase with temperature in a filament lamp?
When the electrical charge flows through the lamp, it transfers some energy to the thermal energy stores of the filament which is designed to heat up. Therefore, the resistance, temperature and current all increase Resistance is directly proportional to temperature
What is an LDR?
Light Dependent Resistor - a resistant dependent on the intensity of light In bright light, the resistance decreases In darkness, the resistance is highest
What is a thermistor?
A temperature dependent resistor In hot conditions, the resistance decreases In cold conditions, the resistance increases
What happens to Pd in a series circuit?
It's shared between all the components
What happens to current in a series circuit?
The current is the same in all components
What happens to resistance in a series circuit?
The total resistance is the sum of all the resistances
What happens to Pd in a parallel circuit?
The Pd is the same in all components
What happens to current in a parallel circuit?
The current is shared between the components, therefore the total current is found by adding up the currents of all the components
What happens to resistance in a parallel circuit?
If you have two resistors parallel, their total resistance is less than the resistance of the smallest of the two resistors
Mains supply is...
AC - Alternating current
Battery supply is...
DC - Direct Current
Alternating Current
The current is constantly changing direction Alternating currents are produced by alternating voltages in which the positive and negative ends keep alternating
UK Mains Supply Voltage
230V
UK Frequency of AC
50Hz (hertz)
Direct Current
Current is always flowing in the same direction Created by a direct voltage
Live Wire
Brown colour Bottom right of the three pin plug Provides the alternating pd from the mains supply - 230V Current flows in through this wire
Neutral Wire
Blue colour Bottom left of the three pin plug Completes the circuit and carries away current Electricity flows out through this wire Around 0V
Earth Wire
Green and yellow colour Middle of the three pin plug Protects the wiring Stops the casing from becoming live Doesn't usually carry a current - only when there's a fault Around 0V
Equation - Energy transferred 1
Energy transferred (J) = Power (W) x Time (s) E=Pt
A 600W microwave is used for 5 minutes. How long (in minutes) would a 750W microwave take to do the same amount of work
600 x (5 x 60) = 180,000J or 180kJ
180,000J = 750W x t
t = 180,000J/750W
t = 240s = 4 minutes
The lower the power rating...
...The less electricity an appliance uses in a given time, therefore it is cheaper to run
Equation - Energy Transferred 2
Energy transferred (J) = Charge flow (C) x Potential difference (V) E=QV
The motor in an electric toothbrush is attached to a 3V battery. 140C of charge passes through the circuit as it is used. Calculate the energy transferred
E=QV
E= 140C x 3V
E = 420J
Equation - Power 1
Power (W) = Potential difference (V) x Current (A) P=VI
Equation - Power 2
P=I²xR Power = current² x resistance
A 1.0kW hair dryer is connected to a 230V supply. Calculate the current through the hair dryer. Give your answer to two significant figures
I=P/V I= 1000/230 I=4.3A
What is the National Grid?
A giant system of cables and transformers that covers the UK and connects power stations to consumers
When does demand for electricity increase?
When it starts to get dark or cold outside When people get up in the morning When people come home from school or work
What is the problem with a high current?
You lose loads of energy as the wires heat up and energy is transferred to the thermal energy stores of the surroundings
What's the cheaper way of transmitting power?
High potential difference and low current - decreases the energy lost by heating the wire and the surroundings
How is static electricity caused?
Friction - when two things rub against each other, electrons from one will rub off on to the other One material will have a positive static charge (e.g. acetate) and the other will have a negative static charge (e.g. polythene)
What subatomic particle moves?
Electrons Positive charges never move - a positive charge is achieved when electrons move away
What increases with a build up of electric charge?
The potential difference between the object and the earth
What is the spark?
When the electrons jump across the gap between the charged particle and the earth if the potential difference becomes too large
How big is the gap for the spark to happen?
Usually fairly small (lightning is an exception)
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Flashcard (21)