P2 Revision Flashcards
Black body radiation
The radiation emitted by a perfect black body
Perfect Black body
A body absorbing all the radiation that hits it
Infrared radiation
Electromagnetic waves between visible light and microwaves in the electromagnetic spectrum
Specific heat capacity
Energy needed to raise the temperature of 1kg of a substance by 1C
Thermal conductivity
Property of a material that determines the energy transfer through it by conduction
How is energy transferred?
Mechanically(when a force does work)
Electrically(work done by moving charges)
By heating
By radiation
Main energy stored
Thermal energy store
Kinetic energy store
Gravitational potential energy
Elastic potential energy
Chemical energy
Magnetic energy
Electrostatic energy
Nuclear energ
What happens when a system changes?
Energy is transferred to/away from the system between different objects in the system or different types of energy stores
Closed systems
When the net change in the total energy of a closed system is alwahs zerk
An example of energy being transferred by heating
Energy’s transferred to the water from the kettle’s heating element to the water’s thermal energy store, causing the temperature of the water to rise
Work done=
Energy transferred
How is energy transferred in a kettle?
Energy’s transferred electrically to the thermal energy store of the kettle’s heating element, which transfers energy by heating to the water’s thermal energy store
How does friction between a car’s brakes and wheels do work?
This friction causes an energy transfer from the wheels’ kinetic energy to the thermal energy store of the surroundings.
How is energy transferred/work done in a collision between a car and stationary object?
The normal contact force between the car and object means energy’s transferred from the car’s kinetic energy store to otner energy stores e,g, the elastic potential and thermal energy stores of the object and car body. Some energy is also transferred away by sound waves.
How is energy transferred/work done when a person throws a ball upwards?
The initial force exerted by the person causes an energy transfer from the chemical energy store of the person’s arm to the kinetic energy store of the ball and the arm.
How can work be done?
When a current flows(work is done against resistance in a circuit), or by a force moving an object.
Kinetic energy store
Anything moving has energy in its kinetic energy store
Kinetic energy=
1/2 x mass x speed2
Gravitational potential energ store
Energy is transferred to this store due to the height it gains above ground
Gravitational potential energy=
Mass x gravitational field strength x height
For a falling object, with no air resistance, energy lost from the gravitational potential energy store=
Energy gained in the kinetic energy store
Impact of air resistance
Air resistance acts on all falling objects, causing some energy to be transferred to other energy stores, like the thermal energy stores of the object and surroundings
Elastic potential energy store
Stretching/squashing an object transfers energy to its elastic potential energy store
Elastic potential energy=
1/2 x spring constant x extension2
Change in thermal energy=
Mass x specific heat capacity x temperature change
How to investigate specific heat capacities
1) You need a block of material with two holes in it.
2) Measure the mass of the block, wrap it in an insulating layer to reduce the energy transferred from the block to the surroundings. Insert the thermometer and heater into the two holes.
3) Measure the initial temperature of the block and set the potential difference of the power supply to be TV, turn on the power supply and start a stopwatch.
4) When you turn on the power, the current in the circuit does work on the heater, transferring energy from the power supply to the heater’s thermal energy store, energy’s transferred to the material’s thermal energy store by heating, causing the material’s temperature to increase.
5) As the block heats up, take readings of the temperature and current every minute for 10 minutes. You’ll find the current throuh the circuit doesn’t change as the block heats up.
6) Turn off the power supply after enough readings and using measurements of the current, and the potential difference of the power supply, calculate power supplied to the heater, using power = potential difference x current. Use this to calculate how much energy is transferred to the heater at the time of each temperature reading with the formula energy = power x time, where t is the time of seconds since the experiment began.
7) Plot a graph of energ transferred to the thermal energy store of the block against temperature and find gradient of the straight part of the graph. The specific heat capacity of the material is 1/(gradient x mass of block).
9) Repeat the experiment with different materials to see how their specific heat capacities compare.
Conservation of energy
Energy can be transferred usefully, stored or dissipated, but is never created or destroyed
Dissipated energy
Wasted energy as the energy stored isn’t used in a useful way. For example, when using a mobile phone, dissipated energy is transferred to the thermal energy store of the phone.
Power
Rate of energy transfer in watts
Power=
Energy transferred/work done(J)
/
Time(s)
Lubricants
For objects rubbed together, lubricants reduce friction between objects’ surfaces as they are liquids which flow easily between objects and coat them. This is effective as frictional forces cause some energy in a system to be dissipated
Conduction
Heating an object transfers energy to the kinetic energy stores of the particles, so they vibrate and collide together and energy’s transferred between the particles’ kinetic energy stores in the process
Thermal conductivity
A measure of how quickly energy is transferred through a material in conduction
Convection
Energetic liquid and gas particles moving from hotter to cooler regions due to heat since liquids and gases can flow, and particles from the warmer/less dense region rise above denser, cooler regions
Examples of thermal insulation in houses
Cavity wall insulation
Cavity walls
Loft insulation
Double-glazed windows
Drought excluders
How do cavity walls provide insulation?
Cavity walls are 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 air gaps can also be filled with a foam, which reduces energy transfer by convection in the wall cavity
How does loft insulation provide insulation?
Loft insulation reduces convection currents(a cycle where air particles are heated, rising, cooling and then sinking) being created in lofts.
How do double glazed windows provide insulation?
They have an air gap between two sheets of glass to prevent energy transfer by conduction through the windows.
How do draught excluders provide insulation?
Draught excluders around doors and windows reduce energy transfers by convection
How to improve efficiency of energy transfers
By insulating objects
By lubricating objects
By making objects more streamlined
Efficiency(in terms of power)=
Useful power output/
Total power output
Efficiency(in terms of energy)=
Useful output energy transfer/Total input energy transfer
How many devices are 100% efficient
NO device is 100% efficient, except electric heaters because all the energy in the electrostatic energy stores is transferred to useful thermal energy stores.
Where ultimately is all energy transferred to?
Thermal energy stores
Examples of non-renewable energh resources
Fossil fuels, like coal, oil and natural gas
What are non-renewable energy resources?
Resources that will eventually run out, but provide most of our energy
Examples of renewable energy sources
The Sun
Wind
Water waves
Hydro-electricity
Bio-fuel
Tides
Geothermal
Advantages of non-renewable energy resources
Provide most of our energy - reliable
Running costs aren’t that expensive
Disadvantages of non-renewable energy resources
Will all run out one day
They all do damage to the environment as they release CO2 into the atmosphere when burned, which adds to the greenhouse effect
Nuclear power always carries the risk of a major catastrophe
Advantages of renewable energy sources
Will never run out
Examples of non-renewable energy resources being used for transport
Petrol and diesel powered vehicles use fuel created from oil.
Coal’s used in old-fashioned steam trains to boil water to produce steam.
Examples of renewable energy sources being used for transport
Venicles run on pure bio-fuels or a mix of a bio-fuel and petrol/diesel
Examples of renewable energy resources used for heating
A geothermal(ground source) heat pump uses geothermal energy resources to heat buildings,
Solar water heaters use the sun to heat water, which is pumped into radiators in the buildings.
Wind power
Each wind turnine has a generator - rotating blades turn the generator and produce electricity
Disadvantages of wind power
Spoil the view
Stop when the wind stops/the wind is too strong
Initial costs high
Advantages of wind power
No fuel costs/minimal running costs
No permanent damage to the landscape
No pollution
Solar cells
Generate electric currents directly from sunlight
Advantages of solar cells
No pollution
Running costs are very low
Disadvantages of solar cells
Only reliable in the daytime
Can’t increase the power output when there’s extra demand
How does geothermal power work?
Slow decay of radioactive elements deep inside the Earth is the source of most of the energy. Can generate electricity/heat buildings directly
Advantages of geothermal power
Little damage to environment
Reliable
Disadvantages of geothermal power
Aren’t many suitable locations for power plants
Cost of building a power plant is high
How does hydroelectric power work?
Building a dam to flood a valley, with water allowed through turbines
Advantages of hydroelectric power
No pollution
Can provide an immediate response to an increased demand for electricity
Disadvantages of hydroelectric power
Big impact on the environment due to the flooding of the valley
Reservoirs look unsightly when they dry out
How does wave power work?
Wave-powered turbines around the coast are connected to a generator
DisAdvantages of wave power
Disturb the seabed and habitats of marine animals
Are a hazard to boasts
Advantages of wave power
No pollution
No fuel costs/minimal running costs
How do tidal barrages work?
Tidal barrages are big dams built across river estuaries. As the tide comes in it fills up the estuary. The water is then allowed out through turbines at a controlled speed.
Advantages of tidal power
Reliable - tides occur twice a day without fail, occur near the predicted height
No pollution
Disadvantages of tidal power
Height of tide is variable so lower tides provide less energy than bigger tides.
Don’t work when the water level is the same either side of the barrage - this occurs four times a day
Bio-fuels
Renewable, carbon neutral energy resources created from either plant products or animal dung
Advantages of biofuels
Reliable - crops take a short time to grow, different crops are grown all year round.
Supposedly carbon neutral
Trends in energy use
Since the beginning of the 21st century, electricity use in the UK has been slowly decreasing as we make our appliances more efficient and are more careful with energy use in our homes. We try to increase our use of renewable energy resources, since non-renewables run out, and pressure from other countries/public mean the government introduced targets that put pressure on energy providers to build new power plants that use renewable resources to ensure they don’t lose business and money.
How is the use of renewables limited
Building renewable power plants is expensive and costs money paid either by customers in their bills, or through government and taxes, people may not be able to afford to do this.
Research on improving the reliability and coet of renewables takes time and money
Even if new power plants are built, there are arguments over where to put them and that some like wind power plants are unethical
Disadvantages of biofuels
Can’t respond to immediate energy demands
Cost of refining biofuels is very high
Examples of non-renewable energy resources used for heating
Natural gas used to heat water, which is pumped into radiators at home.
Electric heaters use electricity generated from non-renewable energy resources.
Action and purpose of a solar panel
Water is heated by radiation from the sun and this water’s used to heat buildings
Payback time
Total spent/annual saving
What affects the amount of energy transferred in solar panels?
Cloud cover
Angle of tilt of cells
How can global warming caused by fossil fuels be reduced?
Carbon capture
Planting more trees
Reasons the amount of electricity use decreased
Energy efficient lighting
Increased energy cost
Why does voltage need to be high in overhead cables?
By increasing the voltage the current’s reduced, which reduces the energy/power loss from the cable
How to improve the efficiency of devices
Lubricate the moving parts to reduce friction.
In circuits, use wires with little electrical resistance as the resistance of a wire causes the wire to get hot when a current passes through it.
Streamline the shapes of moving objects to reduce air resistance, which transfers wasted energy from an object to surroundings
Cut out noise(e.g. tighten loose parts to reduce vibration)
Electric heater
Useful energy - Energy heating the surroundings
Waste energy - Energy emitted from the glowing filament
Hairdryer
Useful energy - Kinetic energy of the air driven by the fan
Wasted energy - Sound of fan motor
Electric motor
Useful energy - Kinetic energy of objects driven by motor and gravitational potential energy of objects lifted by motor
Wasted energy - Energy heated the motor
Nuclear power(advantages)
Release more energy per kg of fuel(300000MJ) compared to fossil fuel power stations(30MJ).
Doesn’t release greenhouse gases - uranium releases energy without burning
Nuclear power(disadvantages)
Risk of radiation leaks and catastrophes
Radioactive waste is produced, difficult to dispose of safely and this needs to be stored for many years
Expensive to set up and close down nuclear power stations
How do nuclear power stations work?
1) The fuel in a nuclear power station is uranium/plutonium. The uranium fuel is in sealed cans in the core of the reactor.
2) The nucleus of a uranium atom is unstable and can split in two, with energy transferred from the nucleus when this happens. Because there are lots of uranium atoms in the core, it becomes very hot.
3) The energy of the core is transferred by a fluid(called the coolant) that is pumped through the core.
4) The coolant is very hot when it leaves the core. It flows through a pipe to a heat exchanger, then back to the reactor core.
5) The energy transferred by the coolant is used to turn water into steam in the heat exchanger. The steam drives turbines that turn electricity generators
What could the student use as an insulating layer for the metal block?
Newspaper/bubble wrap/cotton wool
What happens to the energy wasted by the light bulb?
It’s transferred to the surroundings by heating
Why is low thermal conductivity an advantage?
Lower rate of energy transfer
Which type of fossil fuel power station has the shortest start-up time?
Gas(burning)
Why do scientists develop new energy resources?
Most energy resources have negative environmental effects
