- Created by: Emzibobble
- Created on: 03-04-12 12:27
Heat radiation is the transfer of heat energy by infrared radiation (IR).
Conduction and convection transfer of energy by paricles.
Conduction is heat tranfer in solids. Convection is heat transfer in Liquids and gases.
IR emmited by solids, liquids and gases. Any object can both emit and absorb IR.
An object that is hotter than surroundings emits more radiation than is absorbed. So an abject thats cooler than its surroundings absorb more radiation than it emits.
Dark, matt surfaces absorb IR. Light, shiny surfaces emit IR.
Kinetic theory and conduction
Solids- strong forces, close together, fixed regular arrangment. Not a lot of energy, vibrate in fixed positions.
Liquids- weaker forces, close togehter, an move past each other and irregular arrangements. More energy than solids random directions at low speeds.
Gases- almost no force of attraction between particles, more energy, free to move, random directions at high speeds.
conduction of heat
Condusction of heat energy is the process where vibrating particles pass on their extra kinetic energy to neighbouring particles.
Metals are good conductors because they have free electrons.Heat carried in metals by colliding free electrons.
Convection of heat- liquids and gases only.
Convection occurs when the more energetic particles move from the hotter region to the cooler region to the cooler region - and take their heat energy with them.
Convection currents are all about changes in density.
Heating a room with a radiator relies on onvection currents too. Hot, less dense air by the radiator rises and denser, cooler air flows to replace it.
Condensation and evaporation
Condensation and evaporation are changes of state. Evaporation is when liquid changes to gas (reason why damp clothes dry on washing line). Condensation is when gas changes to liquid (reason why windows go foggy on cold day).
Evaporaton - Particles in a liquid have different energies. Some will have enough energy to escape from liquid to be a gas. Remaining particles in liquid have lower average kinetic energy than before, liquid cools down as evaporation happens. This is why sweating cool you down. Sweat asorbs energy from skin so it continues to evaporate.
Condensation- Particles in a gas have different energies. Some may not have enough energy to remain as separate particles, especially if gas is cooled down. They come close together and bonds form between them. Energy is released when this happens. This is why steam touching your skin can cause scalds: not only is the steam hot, but energy is released into your skin as the steam condenses.
Rate of heat transfer
Bigger the surface area the quicker the transfer of heat e.g radiator.
The bigger the difference in temperature between an object and its surroundings, the greater the rate at which heat energy is transferred.
Other factors also affect the rate at which an object transfers energy by heating. These include the:
- surface area and volume of the object
- material used to make the object
- nature of the surface that the object is touching.
Energy Efficiency in the home
Payback time = initial cost/ annual saving
Cavity wall insulation - foam squirted into the gap between the bricks reduces convection and radiation. across the gap.
loft insulation - reduces conduction and radiation.
Draught- proofing - strips of foam and plastic around doors and windows to stop draughts reduces convection.
hor water tank jacket reduces conduction and radiation.
thick curtains reduces conduction ans radiation.
U- values - heat tranfers faster through materials with higher u-values than through materials wit low u- values. Better the insulator lower the u- values.
Specific Heat Capacity
Tempreture ans and heat are different.
Temperature is a measure of how hot something is. Measured in °C.
Heat is measure of thermal energy contained in an object. Measured in J.
When heat energy is transferred to an object, the temp increases depends on:mass of object, substance object made from and amount of energy transferred to object.
E= m x c x 0
E energy transferred in joules. m mass in kg. c specific heat capacity in J/kg °C. 0 is difference in temperature.
Electrical energy- whenever current flows. Light energy- sun, light bulbs, etc. Sound Energy- loudspeakers or anything noisy. Kinetic energy- anything moving. Nuclear energy- released from nuclear reactions. Thermal energy- flows from hot objects to colder ones. Gravitational potential energy- possessed with anything that can fall. Elastic potential energy- stretched springs, elastic, rubber bands, etc. Chemical energy- possessed by foods, fuels, batteries.
Energy transferred(kilowatt-hour, KWh) = power(kilowatt, KW) x time(hour,h).
Cost= no.of units x price per unit
efficiency of machines
No devise is 100% efficient and the wasted energy is usually spread out as heat.
Efficient = useful energy out
total energy in power = energy
Heat exchanges reduce the amount of heat energy that is "lost". They di thus by pumping a cool fluid through thr escaping heat. The temperature of this fluid rises as it gains heat energy. The heat energy in the fluid can then be converted into a form of enerfy that is useful again - either in the original device or other useful functions. eg some heat from cars engine can transfer to the air thats used to warm passenger compartment.
see page 22
Energy sources and power stations
Non-renewable: Coal, oil, natural gas and nuclear (uranium and plutonium).
Renewable: Wind, waves, tides, hydroelectric, solar, geothermal, food and biofuels.
chemical energy -> heat energy -> kinetic energy -> electrical energy
fuel ->boiler->turbine -> generator -> grid
renewable energy sources - Wind power (wind turbin
Wind power- lots of wind turbines in exposed places eg on moors and coasts. Each turbine has own generator inside. Electricity is made by wind turning blades which turn generator. No pollution (except when turbine is made).
They do spoil the view, eg 1500 wind turbines are needed to replace one coal fired power station and 1500 turbines need a lot of ground. Very noisy (annoying to live near them). No power when wind stops, impossible to increase supply when there's extra demand. Initial costs high, but no fuel costs and minimum running costs.
There isn't any permanent damage to landscape - if you remove turbines.
Renewable energy sources - solar cells
Solar cells generate electricity using sunlight.Often best being used for calculators and watches, as they don't need much electricity.
Solar panels are often used in remote places such as, australian outback. These power electric road signs and satellites. No pollution (after manufactured). Reliable in sunny places during the day time. Can also be cost effective in cloudy Britain.
Initial costs are high, but after that it is free for a lifetime and there is almost no running costs.
Solar cells are usually to power little things such as an individual house. Often not practical or too expensive to connect to national grid.
Renewable energy sources - Hydroelectric power
Hydroelectric power usually requires the flooding of a valley by building a big dam. Rainwater is caught and allowed through turbines. No pollution. But there is a big impact on the environment due to flooding a valley and possibly loss of habitat for some species. Reservoirs can also look bad when dried up.
water stored -> through dam -> turns turbine -> turns generator -> national grid.
Can provide immediate response to an increase demand for electricity. Reliability is no porbs unless there is drought. Initial costs high, butno fuel and minimal running costs. Useful way on a small scale for remote areas.
Renewable energy sources - Pumped storage
Most large power stations have huge boilers, these have to be kept running all night. Even though demand in very low, this means there is a surplus of electricity at night.
It is difficult to find a way of storing spare energy for later use.Pumped storage is one of the best storage.
In pumped storage, spare night-time elecricity is used to pump water up to a higher reservoir. This can be released quickly during times of great demand.
Pumped storage uses the same idea as hydroelectric power, but it isn't a way of generating power - it is simply a way of generating power (it is just storing energy which is already generated).
Renewable energy sources - wave power
Needs lots of little wave-powered turbine located around the coast. When waves go in to shore, provides up and down motion which can drive a generator.
No pollution. Main problems are it spoils the view and is hazard to boats. Fairly unreliable as waves die own when wind drops.
Inital costs are high, no fuel costs and minimal running costs. Can never likely provide energy on a large scale, but useful on small islands.
Renewable Energy- Tidal Barrages
Uses sun and moon's gravity - source of energy. Tidal barrages are big dams built across river estuargies, with turbines in them. As the tide comes in it fills up the estuary to a height of several metres- it also drives the turbines at a controlled speed.
No pollution. Main problems are preventing free access by boats, Spoiling the view and altering the habitat of wildlife. Tides are pretty reliable, happens twice a day without fail and near predicted height.
Only drawback - height of tide is the variable, e.g lower tide = less energy than bigger spring tides.They also don't work when the water level is the same either side of the barrier, this happens four times due to tides. These are excellent for storing energy ready for times of peak demand.
Initial costs are moderately high, no fuel costs and minimal running costs. Some of the most suitable estuaries has potentiak for generating a significant amount of energy.
Renewable energy sources - geothermal energy
Heat from underground. Only possible in volcanic areas where hot rocks lie quite near the surface, e.g 7km. The source of much of the heat is the slow decay of various radioactive elements , including uranium that is deep inside the Earth.
Hot rocks underground -> hot water and steam rise from the Earth -> Steam -> turbine -> generator -> grid
In some places, geothermic heat is used to heat buildings up directly, without the need to turn it into electrical energy.
Main drawback is there is not a lot of suitable locations for the power plants. Cost of building a power plant is high compared to what energy you can get out of it.
renewable energy sources. Made from plants and waste. Generate electricity just like fossil fuel (burn to heat up water etc).
Also be used in some cars like petrol (fossil fuel). Can be solids (straw,nutshells etc) , liquids (ethanol) and gases (methane).
We can get biofuel from organisms that are still alive or dead (but onlt organisms that have been living much more recently than fossil fuels).
E.g Crops like sugar cane can be fermented to make ethanol, or plant oils can be modified to produce biodiesel.
Energy sources and the environment
All three fossil fuels release co2 into the atmosphere when they are burned. Coal releases the most CO2 then oil then gas. This CO2 adds to to the greenhouse effect and contributeds to global warming.
Burning coal and oil releases sulfer dioxide causing acid rain. Acid rain can be harmful to trees and soils and can have far-reachingefects in ecosystems. Acid rain can e reduced by taking out the sulfer before burning it, or clean up emissions.
Coal mining makes a mess of landscape, especially "open-cast mining". Oil spillages cause serious environmental problems, affects mammals and birds that live in and around sea. We try and avoid them but,they will always happen. Nuclear power is clean but the waste is dangerous and difficult to dispose.
Nuclear fuel is relativiely cheap but overall costs high (power plant and final decommissioning). Nuclear carries risk of catastrophe like Chernobyl disaster in 1986.
bio-fuels have disadvantages too......
There is still a debate into impact on environment, once energy of production is considered. Plants are produced, absorbed carbon dioxide from atmosphere as they are growing. When waste is burnt this co2 is re-released into atmosphere. So it has a natural effect atmospheric co2 levels. Also creates methane if animals eat plants during the process.
Some regions large amounts of forest is cleared to grow bio-fuels, species lose habitat. Burning plants also causes co2 and methane emissions. Bio-fuel use is limited depends in land available for bio-fuels.
CCS - carbon capture and storage.
Comparison of energy resources
running fuel costs - Renewable is usually lower in running costs as there is no fuel involved.
Reliability issues - Non-renewable are reliable until they run out. Renewable depends on the wheather which is pretty unreliable in the UK. Except tidal power and geothermal.
location issues - wind (windy coasts and moors), oil (coast), nuclear( away from people and near water), gas (anywhere), hydroelectric (hilly and rainy somewhere it can flood), and power station (near things they can collect the right fuel).
Environmental - Atmospheric pollution, visual pollution, using up resources, noise pollution, habitat, leisure activities. Nuclear is waste and hydroelectric dams bursting.
Consider - damage to environment, impact on local communities, permission, long- running power station, set-up time and cost of shutting down power plant.
gas -fired power stations used more than coal and oil as gas has more left and doesn't pollute as much.
set-up costs - renewable energy sources = bigger power stations (bigger the station the more expensive it is).
set-up/decommissioning time - affected by size, complexity, planning issues (coastline ruined), nuclear longest and gas is the quickest to set up.
Electricity and the national grid
To get 400,000 volts we need to transmit power using transformers and pig pylons with huge insulators - it is still cheaper. Step-up tranformers bring it to pylons, step-down transfprmers brings it to the houses.
Supply demand The national grid needs to generate ans direct all energythe country needs, as demands keep increasing. Demands could be reduced by consumers using energy effecient appliances and being more careful not to waste electricity.
Disrtibuted using the natioanl grid - takes electrical energy from power stations to where needed.
Generated anywhere, supplied anywhere.
There is a huge amount of pewer needed nowadays.
High current or high voltage, high current loses energy in heat for cables so it is cheaper to have a bigger voltage.
speed = Frequency X wavelength (speed in m/s, frequency in Hz and wavelength in M)
Most waves are transverse: light and EM waves, ripples in water, waves on strings, slinky spring. On transverse waves the vibrations are perpendicular (90 degrees) to the directionof energy trenfer of the wave.
Longitudinal waves are: sound waves, shock waves, plinky spring (when you push the end). Shows compression. In longitudinal waves vibrational are parallel tp direction of energy transfer of the wave.
Wave properties and Refraction
All waves can be reflected, refracted and diffracted.
Reflection of light allows us to see objects. Light bounces off them into our eyes.
When light travels at same direction on uneven surface light reflects off at different angles.
Angle of incidence = Angle of reflection
Refraction - Which means they go through a new material but change direction.
If a wave hits a boundary straight on it carries on in the same direction. Different medium at angle it changes direction (it has been refracted).
Only refracted if they meet at a new medium, some of light is reflected, but a lot passes through gass and is refracted.
Diffraction of waves
Diffraction means the spreading out of waves when they pass through a gap or around an obstacle. This is how you can hear the radio outside of the room.
Narrower the gap, the greater the defraction is.
When waves pass through a gap, their wavelength is the same as it was before it passed through the gap.
If radio waves do not diffract enough when they go over hils, radio and TV signals will be poor.
Radio waves -> microwaves -> infrared -> visible light -> ultra violet -> x rays -> gamma rays
EM waves vary from 10 (to the power of) -15 m ----> 10 (to the power of) 4 m
All waves travel the same speed in a vacuum e.g space.
Higher the frequency, shorter the wavelength.
Long wave radio wavelengths can diffract around hulls into tunnels etc.
Difraction makes radio signals able to recieve.
Radio and TV both have short wavelength.
Visible light - ROYGBIV
EM waves and their uses
Communication to and from satellite (satellite TV and phone) uses microwaves. You need to use microwaves which can pass easily through the earth's wattery atmosphere. Radio waves can't do this.
Satellite TV is transmitted into space by using a transmittor. It is then picked up by the satellite's reciever dish which is orbiting thousands of kilometres above the Earth. Then the satellite transmits the signal back to Earth in a different direction where it is recieved by a satellite dish on the ground.
Mobile phones also do this between your phone and the nearest transmitor. If the water heats up and they are in your cells , you might start to cook - this is why many people think using your phones a lot or being near a mast could damage your health.
Infrared waves are used for wireless remote controllers. Optical fibres (like in phone lines) can carry data over long distances quickly. They use both visible light and infrared.
Sound waves are caused by vibrating objects. it is a series of compressions. They are a type of longitudinal wave. Sound will travel through inner ear and then eardrum to here it. The denser the medium, the faster the sound travels through it. Sound travels faster in solids than liquids and faster in liquids than gases. Sound can't travel in space as in a vacuum they're no particles.
Sound waves can be reflected by hard flat surfaces. If carpets and curtains are in it will absorb some of the sound. Sound waves will also refract (change direction) as thet enter different media. enter denser material, they speed up.
High frequency - high pitch (shorter wavelength) Low frequency - low pitch
Frequency is number of complete vibrations every second. 100Hz vibrates 100 times per second. (KHz - 1000 Hz and MHz - 1 000 000 Hz)
loudness of sound depends on amplitude of sound wave. Bigger amplitude louder the sound.
Origin of th universe
All galaxies seem to be moving away from each other evidence is....
Different chemical elements absorb different frequences of light. Each element produces a specific pattern of dark lines at the frequency that it absorbs in the visible spectrum. When we look at light from distant galaxies we can see the same patterns but at slightly lower frequencies than they should be. They shift toward the red end of spectrum - this is why its called red shift. This is just like the the doppler effect.
When something that emits waves moves towards you or away from you, the wavelength and frequencies appear different, Compared to something when stationary.
Frequency of a source moving towards you will seem higher and wavelength shorter. Frequency of something moving away will seen lower and wavelength shorter. Doppler effect happens in both longitudinal waves and transverse waves.
Origin of the universe
All the matter and energy in the universe must have been compressed into a very small space. Then it exploded from that single point and started expanding, expansion is still happening even after 14 billion years.
The "steady state" theory says that the universe has always exsisted as it is now, and it always will do. This is because the universe is pretty much the same everywhere.
The discovery of the cosmic microwave background radiation (CMBR) some years later was strong evidence that the big bang was the more like explantion of the two. The big bang is the only theory that can explain CMBR. This is because after the big bang the the universe was extremely hot but after the universe has expanded it has cooled and now seen as microwave radation.