P1b

-Almost all the electricity used is generated in power stations 

-In coal or oil-fired power stations, and in most gas-fired power stations, fossil fuels are burnt, which releases heat, the heats up water producing steam, the steam turns a turbine and the turbine is used to generate electricty

-In a gas fired power station, natural gas is burnt directly in a gas turbine engine. This heats the air drawn into the engine, it produces a powerful jet of hot gases and the air that drives the turbine. A gas-fired turbine can be switched on very quickly

-A biofuel is any fuel obtaine from living or recently living organsims such as animal waste or woodchip

-Other biofuels include methane, ethanol, straw, nutshells and woodchip 

A biofuel is;

• Renewable- becuase its biological source continues to exist and never dies out as a species 
• Caron- neutral- the carbon takes in from the atmosphere as carbon dioxide can balance the amount released when it is burned 

-The fuel in a nuclear power station is uranium or plutonium

-The uranium fuel is in sealed cans in the core of the reactor. The nucleus of uranium atom is unstale and can split in two. Energy is released when this happens, this process is called nuclear fission 

-The energy of the core is transferred by a fluid (called the 'coolant') that is pumped through the core

-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 

-The energy of the coolant is used to turn water into steam in the heat exchanger. The steam drives the turbines that turn electricity generators 

-Energy from the wind and other natural sources such as waves and tides is renewable energy

-They are also carbon neutral 

-WIND POWER;

-A wind turnbine is an electricty generator at the top of a narrow tower.The force of the wind drives the turbine's blade around, this turns a generator

-WAVE POWER;

-A wave generator uses waves to make floating generator move up and down. This motion turns the generator to generate electricity. A cable between the generator and the shore delivers electricity to the grid system

-Wave generators need to withstand storms and they don't produce a constant supply of electricity. Also, lots of cables are needed along the coast to conenct the wave generator to the electricity grid which can spoil the landscape

-HYDROELECTRIC POWER;

-We can generate electricity when rainwater collected in a reservoir  (or water pumped in a storage scheme) flows downhill. The flowing water drives turbines that turn electricity generators and the foot of the hill 

-TIDAL POWER;

-A tidal power station traps water from each high tide behind a barrage. We can then release the high tide into the sea through turbines which drive the generators in the barrage 

-Solar energy transfers energy to you from the sun

-We can use the Sun's energy to generate elecricity using solar cells

-We can also use the Sun's energy to heat water directly in solar heating panels 

-Solar cells at present convert less than 10% of the solar energy they absorbs into electrical energy

-They are useful where we only need small amounts of the electricity or in remote places

-They are very expensive to buy even though they cost nothing to run 

-We need lots of them, and plenty of sunshine, to generate enough power to be useful 

-A solar heating panel heats water that flows through it

-Even on a cloudy day in Britain, a solar heating panel on a house roof can supply plenty of water

-A solar power tower uses thousands of flat mirrors to reflect sunlight onto a large water tank at the top of the tower 

-The mirrors on the ground surround the base of the tower

-The water in the tank is turned into steam by the heating effect of the solar radiation directed at the water tank 

-The steam is piped down to ground level where it turns electricity generators 

-The mirrors are controlled by a computer so they track the sun 

-Geothermal energy comes from energy released by radioactive substances deep within the Earth 

-The energy released by these radioactive substances heats the surrounding rock 

-As a result, energy is transferred by heating towards the Earth's surface 

-We can build geothermal power stations in volcanic areas or where there are hot rocks deep below the surface

-Water gets pumed down to these rocks to produce steam 

-The steam produced drives electricity turbines at ground level 

-In some areas, we can heat buildings using geothermal energy directly. Heat flow from underground is called ground heat 

-It can be used to heat water in long lengths of underground pipes. The hot water is then pumped round the building

-When we burn coal, oil or gas, greenhouse gases such as carbon dioxide are released, which cause global warming 

-Burning fossil fuels can also produce sulfur dioxdie which causes acid rain. We remove the sulfur from a fuel before burning it to prevent this 

-Fossil fuels are non-renewable 

-Carbon capture and storage could be used to stop carbon dioxide emissions into the atmosphere from fossil fuel power stations

Advantages;

• No greenhouse gases 
• More enrgy produced 

Disadvantages;

• Used fuel rods contain radioactive waste, which has to be stored safely for centuries 
• Nuclear reactors are safe in normal operation. However, an explosion could release radioactive material

Advantages;

• They will last forever 
• They don't produce greenhouse gases or acid rain 
• Don't create radioactive waste products 
• Can be used where connection to the National Grid is uneconomic 

Disadvantages;

• Wind turbines can create noise which disturbes people nearby 
• Wind turbines are not 100% efficient-not always windy 
• Tidal barrages affect river estuaries and the habitats of creatures and plants there 
• Hydroelectric schemes need large reservoirs of water, which can effect nearby plant and animal life, habitats are often flooded to create dams
• Solar cells would need to cover large areas to generate large amounts of power 

-The National Grid is a network of cables that distributes electricity from power stations to homes and other buildings 

-The National Grid's voltage is 132 000V or more, because transmitting electricity at a high voltage reduces power loss, making the system more efficient 

-Step-up transformers are used to increase the voltage to the grid voltage 

-Step-down transformers at local substations to step the gird voltage down to 230V for use in homes and offices 

-The electrical power supplied to any appliance depends on the appliance's current and voltage 

-To supply a certain amount of power, we can lower the current if we raise the voltage, which is what a step-up transformer does 

-A step-up transformer raises the voltage, so less current is needed to transfer the same amount of power 

-A lower current passes through the grid cables, so energy losses due to the heating effect of the current are reduced to almost zero 

-But we need to lower the voltage at the end of the grid cables before we can use mains electricity at home 

-The start up times depends on the type of power station 

-Natural gases-> oil-> coal-> nuclear 

(Shortest start up time -> longest start up time)

-Renewable energy resources are unreliable;

• Hydroelectric-upland reservoir could run dry 
• Wind, waves- wind and waves too weak on very calm days 
• Tidal-height of tide varies on a monthly and yearly cycle 
• Solar- no solar energy at night, variable during day 

-The vibrations of a transverse wave are perpendicular to the direction in which the waves transfer energy 

-The vibrations of a longitudinal wave are parallel to the direction in which the waves are travelling 

-Examples of mechanical waves are; sound waves and water waves 

-Examples of electromagnetic waves; light waves, radio waves, microwaves 

-The amplitude of the wave is the height of the wave crest or the depth of the wave trough from the middle, which is the position of the rope at rest 

-The bigger the amplitude of the waves, the more energy the waves carry

-the wavelength of the waves is the distance from one wave crest to the next crest 

-Frequency-> the number of wavecrests passing a fixed point every second, measured in Hertz (Hz)

-Speed of wave-> distance travelled by a wave crest or a wave trough every second 

-Wave speed (metre/second, m/s) = frequency (hertz, Hz) x wavelenght (metre,m) 

-Law of reflection;

• The perpendicular line to the mirror is called the normal line
• The angle of incidence is the angle between the incident ray and the normal 
• The angle of reflection is the angle between the reflected ray and the normal 

the angle of incidence=the angle of reflection 

-The image formed by a plane mirror is virtual, upright and laterally inverted (back to front) 

-A virtual image can't be projected onto a screen 

-A image on a screen is described as a real image because it's formed by focusing light rays onto the screen 

-Refraction-> the change of direction of a light ray when it passes across a boundary between two transparent substances 

Refraction rules;

• Changes direction towards the normal when it travels from air into glass, the angle of refraction (r) is smaller than the angle of incidence (i) 
• Changes direction away from the normal when it travels from glass into air, the angle of refraction (r) is greater than the angle of incidence (i) 

-Diffraction is the spreading of waves when they pass through a gap or move past an obstacle 

-An ultrasonic scan can be made of a baby in the womb 

-The ultrasonic waves spread out from a hand-held transmitter and then reflect from the tissue boundaries inside the womb 

-The singal from a TV transmitter mast is carried by radio waves 

-Sound waves cannot travel trhough a vaccum 

-Echo;

• if the walls are covered in soft fabric, the fabric will absorb sound instead of reflecting it, so no echo will be heard 
• if the wall surface is uneven, echos will not be heard because the reflected sound is 'broken up' and scattered 

-The warmer the air, the greater the speed of sound 

-Increasing the loudness of a sound increases the amplitude of the waves,so the waves on the screen become taller 

-Increasing the frequency of a sound (number of waves per scond) increases its pitch, making more waves appear on screen 

-Electromagnetic waves are electric and magnetic disturbances that transfer energy from one place to another 

-Electromagnetic waves do not transfer matter

-The energy they transfer depends on the wavelength of the wave 

-Radio waves, microwaves, infrared radiation, visible light, ultraviolet, xrays, gamma rays 

-Light from the sun is called white light, because it has all the colours of the visible spectrum in it (red, orange, yellow, green, blue, indigo, violet)

-The wave length increases across the spectrum as you go from violet to red 

-In a film camera, the light is focused by the camera lens on to a light sensitive film. The film then needs to be developed to see the image of the objects that were photographed

-In a digital camera, the light is focused by the lens onto a snesor. This consists of thousands of tiny light-sensitive cells called pixels. Each pixel gives a dot of the image. The image can be seen on a small screen at the back of the camera.When a photo is taken, the image is stred electronically on a memory card 

-Optical fibres in communication systems use infrared radiation instead of light, because infrared radiation is absorbed less than light in the glass fibres 

-Remote contol handsets for a TV and video equipment transmit signals carried by infrared radiation. When you press a button on the handset, it sends out a sequence of infrared pulses 

-Infrared scanners are used in medicine to detect 'hot spots' on the body surface. These hot areas can mean the underlying tissue is unhealthy

-You can use infrared cameras to see people and animals in the darkness 

-Microwaves are used for communications e.g satellite tv, because they can pass through the atmosphere and reach satellites above the Earth

-We also use them to beam signals from one place to another because they don't spread out as much as radiowaves 

-Radio wave frequencies range from about 300 000Hz to 3000 million Hz

-Radio waves are longer in wavelength and lower in frequecny than microwaves 

-Radio waves are used to carry radio, TV and mobile phone signals 

-Radio waves are emitted from an aerial when we apply an alternating current voltage to the aerial

-The frequency of the radio waves produced is the same as the frequency of the alternating voltage 

-When the radio waves pass across a reciever aerial, they cause tiny alternating voltage in the aerial 

-The frequency of the alternating voltage is the same as the frequency of the radio waves recieved 

-The aerial is connected to a loud speaker, the alternating voltage from the aerial is used to make the loudspeaker send out sound waves 

-The radio and microwave spectrum is divided into bands of different wavelength ranges, because the shorter the wavelenght of the waves;

• the more information they can carry
• the shorter their range (due to increasing absorption by the atmosphere)
• the less they spread out (because they diffract less)

-Microwaves are used for satellite phone and TV links and satellite TV broadcasting, becuase microwaves can travel between satellites in space and the ground. Also, they spread out less the radio waves do so the signal doesn't weaken as much 

-Radio waves of wavelengths less than 1 metre are used for Tv broadcasting from TV masts becuase they can carry more information than longer radio waves 

-Radio waves of wavelengths from about 1 metre up to about 100 metres are used by local radio stations because their range is limited to the area round the transmitter 

-Radio waves of wavelengths greater than 100 metres are used by national and international radio stations becuase they have a much longer range than shorter wavelength radio waves 

-Optical Fibres are very thin glass fibres used to transmit signals carried by light or infrared radiation

-The light rays can't escape from the fibre, when they reach the surface of the fibre, they are reflected back into the fibre 

-Opitcal fibres carry much more information in comparison to radio waves and microwaves becuase, light has a much smaller wavelength than radio waves so can carry much more pulses of waves 

-Optical fibres are more secure because the signals stay in the fibre 

-The Doopler Effect is the change in the observed wavelength of waves due to the motion of the source of the waves 

-Christian Doopler discovered the effect in 1842 using sound waves 

-He demonstrated it by using an open railway carriage filled with trumpeters 

-The spectators had to listen to the pitch of the trumpets as they sped past

-Another example, is the red-shift of the light from a distant galaxy moving away from us 

-We can tell from its spectrum if a star is moving away or towards us, because;

• the light waves are stretched out if the star or galaxy is moving away from us, the wavelength increases, this is called red-shift because the spectrum of light is shifted towards the red part of the spectrum 
• the light waves are squashed together if the star or galaxy is moving towards us, the wavelength is reduced, this is called blue-shift because the spectrum of light is shifted towards the blue part of the spectrum 

-The faster a star or galaxy is moving, the bigger the shift is 

-In 1929 Edwin Hubble dicovered that;

• the light from distant galaxies was red-shifted 
• the further away a galaxy is from us, the bigger its red-shift 

He concluded that;

• the distant galaxies are moving away from us 
• the greater the distance a galaxy is from us, the greater the speed is at which it is moving away from us 

-The Big Bang theory was put forward to explain the expansion of the universe, it states that;

• the universe is expanding after exploding suddenly in a Big Bang from a very small initial point
• space, time and matter were created in the Big Bang 

-Many scientists disagree with the Big Bang theory, they put forward an alternative theory, the Steady State theory

-The scientists said that the galaxies are being pushed apart, they thought that this is caused by matter entering the universe through 'white holes'

-Cosmic microwave background radiation;

• it was created as high-energy gamma radiation just after the Big Bang
• it has been travelling through space since then 
• as the universe has expanded, it stretched out to longer and longer wavelengths and is now microwave radiation 
• it has been mapped out using microwave detectors on the ground and on satellites