P2 - Living for the Future (OCR Gateway Science B)

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  • Created by: lilyemma
  • Created on: 18-04-17 20:29

Using the Sun's Energy I

The sun is the ultimate source of loads of our energy:

  • Every second for the last few billion years or so, the Sun has been giving out loads of energy - mostly in the form of heat and light.
  • Some of that energy is stored here on Earth as fossil fuels (coal, oil and natural gas). And when we use wind power, we're using energy that can be traced back to the Sun (the Sun heats the air, the hot air rises, cold air goes in to take its place [wind] and so on)
  • But we can also use the Sun's energy in a more direct way - with photocells and solar energy

You can capture the Sun's energy using photocells:

  • Photocells (solar cells) generate electricity directly from sunlight.
  • They generate direct current (DC) - the same as a batttery. Direct current just means the current flows the same way round the circuit all the time - not like mains electricity in your home (AC), which keeps switching direction.
  • Photocells are usualy made of silicone - a semiconductor. when sunlight falls on the cell: the silicon atoms absorb some of the energy, knocking loose some electrons, these electrons then flow round a circuit - which is electricity. 
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Using the Sun's Energy II

The current and power output of a photocell depends on:

  • its surface are (the bigger the cell, the more electricity it produces)
  • the intensity of the light (brighter light = more electricity)
  • the distance from the light source (the closer the cell, the more intense the light hitting it will be.
  • Photocells have lots of advantages: There are no moving parts - so they're sturdy, low maintenance and last a long time. You don't need power cables or fuel (your digital calculator doesn't need to be plugged in/ fuelled up). Solar panels won't run out (it's a renewable energy resource), and it doesn't pollute the enviroment.
  • But there's one major disadvantage - no sunlight, no power. So they're rubbish at night, and not so good when the weather's bad.

Curved mirrors can concentrate energy from the Sun:

  • Curved mirrors focus the Sun's light and heat.
  • A single curved mirror can be used as a solar oven.
  • Large curved mirrors (or combination of ltos of smaller mirrors) can be used to generate steam to produce electricity.
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Using the Sun's Energy III

  • All devices that collect energy from the Sun (mirrors, solar cells and solar panels) are most efficient if they track the Sun's movement across the sky.
  • If collectors are pointed directly at the Sun then they can capture the maximum amount of light and heat.
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Solar and Wind Power I

Passive solar heating - no complex mechanical stuff:

  • Passive solar heating is when energy from the Sun is used to heat something directly.
  • You can reduce the energy needed to heat a building if you build it sensibly and think about passive solar heating - eg: it can make a big difference which way the windows face.
  • Glass lets in heat and light from the Sun, which is absorbed by things in a room, heating them up.
  • The light from the Sun has a short wavelength, so it can pass through the glass in a room.
  • But the heated things in a room emit infared radiation of a longer wavelength, which can't escape through the glass - it's reflected back instead, just like in a greenhouse.
  • So this 'greenhouse effect' works to heat, and keep heat inside a building.
  • Solar water heaters use passive solar heating too - the glass lets heat and light from the Sun in which is then absorbed by the black pipes and heats up the water (which can be used for washing or pumped to radiatiors to heat the building).

Wind farms - lots of little wind turbines:

The Sun is the reason we have wind - it's also the reason we have wind farms.

  • Wind power involves putting lots of wind turbines up in exposed places - like on moors, the coast or out at sea.
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Solar and Wind Power II

  • Energy from the Sun heats the atmosphere which causes convection currents which produces wind.
  • Wind turbines convert the kinetic energy or moving air into electricity. The wind turns the blades, which turn a generator.

Wind is a renewable resource:

Wins turbines, like any energy source, have advantages and disadvantages (LEARN THESE):

ADVANTAGES:

  • Wind turbines are quite cheap to run - they're tough and reliable and wind is free.
  • Even better, wind power doesn't produce any polluting waste.
  • Wind power is also renewable - the wind's never going to run out.

DISADVANTAGES:

  • You need about 1500 wind turbines to replace one coal-fired power station.
  • Some people think that wind farms spoil the view (visual pollution) and the spinning blades cause noise pollution.
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Solar and Wind Power III

  • Another problem is that sometimes the wind isn't fast enough to generate any power.
  • It's also impossible to increase supply when they're an extra demand.
  • It can be difficult to find a suitable place to build wind turbines - they need to be spaced out and built in places that are windy enough.
  • And although the wind is free, it's expensive to set up a wind farm, especially out at sea.
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Producing and Distributing Electricity I

The national grid connects power stations to consumers:

  • The National Grid is the network of pylons and cables which covers the whole country.
  • It takes electricity from power stations to just where it's needed in homes and industries.
  • It enables power to be generated anywhere on the grid, and then supplied anywhere else on the grid.

All power stations are pretty much the same:

The aim of power station is to convert one kind of energy (eg: the energy stored in fossil fuels, or nuclear energy contained in the centre of atoms) into electricity. Usually this is done in three stages:

  • 1. The first stage is to use the fuel to produce heat which then generates steam - this isthe job of the boiler.
  • 2. The moving steam drives the blades of a turbine...
  • 3. ...and this rotating movement from the turbine is converted to electricity by the generator (using electromagnetic induction).

Most power stations are terribly inefficient - usually more than half the energy produced is wasted as heat and noise (though the efficiency of the power station depends on the source)

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Producing and Distributing Electricity I

The national grid connects power stations to consumers:

  • The National Grid is the network of pylons and cables which covers the whole country.
  • It takes electricity from power stations to just where it's needed in homes and industries.
  • It enables power to be generated anywhere on the grid, and then supplied anywhere else on the grid.

All power stations are pretty much the same:

The aim of power station is to convert one kind of energy (eg: the energy stored in fossil fuels, or nuclear energy contained in the centre of atoms) into electricity. Usually this is done in three stages:

  • 1. The first stage is to use the fuel to produce heat which then generates steam - this isthe job of the boiler.
  • 2. The moving steam drives the blades of a turbine...
  • 3. ...and this rotating movement from the turbine is converted to electricity by the generator (using electromagnetic induction).

Most power stations are terribly inefficient - usually more than half the energy produced is wasted as heat and noise (though the efficiency of the power station depends on the source)

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Producing and Distributing Electricity II

Different power sources have advantages and disadvantages:

  • FOSSIL FUELS - Fossil fuels are burnt to release their heat energ. At the moment, these fuels are readily available, and they're a concentrated source of energy (a little bit of coal gives a bit of heat). But burning fossil fuels causes acid rain and produces carbon dioxide (a greenhouse gas). Also, we buy most of our fossil fuels from other countries - which means we don't have control of the price or supply.
  • BIOMASS - Biomass is stuff from plants (like wood and straw) or animals (their manure) that can be burnt directly, or fermented to produce methane that's also burnt. Biomass is renewable - we can quickly make more by growing more plants and rearing more animals. Burning methane doesn't produce carbon dioxide, but this CO2 that the plants took out of the atmosphere where they were growing - the process is 'carbon neutral' overall. Recently, we've started to use more biomass in the UK. You do not need a lot of biomass to replace one lump of coal, and it takes lots of room to grow it. But we don't need to import straw or poo from other countries.
  • NUCLEAR POWER - Nuclear power stations use the heat released by uranium (or plutonium) atoms as they split during a nuclear reaction.
  • PHOTO CELLS - Photocells absorb energy from the Sun and convert it into electricity.
  • WIND TURBINES - Wind turbines convert energy from the movement of the wind into electricity.
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The Dynamo Effect I

ELECTROMAGNETIC INDUCTION: The creation of a VOLTAGE (and maybe current) in a wire which is experiencing a CHANGE IN MAGNETIC FIELD.

The dynamo effect - move the wire or the magnet:

  • Using electromagnetic induction to transform kinetic energy (energy of moving things) into electrical energy is called the dynamo effect.  (In a power station, this kinetic energy is provided by the turbine.)
  •  There are two different situations where you get EM induction: A - An electrical conductor (a coil of wire is often used) moves through a magnetic field. B - The magnetic field through an electrical conductor changes (gets bigger or smaller or reverses).

If the direction of movement is reversed, then the voltage/current will be reversed too. To get a bigger voltage and current you can increase...

  • The strength of the magnet
  • The number of turns on the coil
  • The speed of movement
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The Dynamo Effect II

Generators move a coil in a magnetic field:

  • Generators rotate a coil in a magnetic field.
  • Every half a turn, the current in the coil swaps direction. (Think about one part of the coil... sometimes it's heading for the magnet's north pole, sometimes for the south - it changes every half a turn. This is what makes the current change direction.)
  • This means that generators produce an alternating current (AC). Turning the coil faster produces not only more peaks, but a higher voltage and current too.
  • The frequency of AC electrical supplies is the number of cycles per second, and is measured in hertz (Hz). In the UK, electricity is supplied at 50 Hz (which means the coil in the generator at the power station is rotating 50 times every second).
  • Remember, this is completely different from the DC electricity supplied by batteries and photocells. 
  • Dynamos on bikes work slightly different - they usually rotate the magnet near the coil. But the principle is exactly the same - they're still using EM induction.
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Supplying Electricity Efficiently I

Electricity is transformed to high voltage before distribution:

  • To transmit a lot of electrical power, you either need a high voltage or a high current. But a higher current means your cables get hot, which is inefficient (as the heat is a waste)/
  • It's much cheaper to increase the voltage. So before the electricity is sent round the country, the voltage is transformed to 400000V (this keeps the current very low, meaning less wasted energy because heating of the cables is reduced)/
  • To increasee the voltage, you need a step-up transformer.
  • Even though you need big pylons with huge insulators (as well as the transformers themselves), using a high voltage is the cheapest way to transmit electricity.
  • To bring the voltage down to safe usable levels for homes, there are local step-down transformers scattered round towns.
  • This is the main reason why mains electricity is AC - so that the transformers work. Transformers only work on AC.

Power stations aren't very efficient:

  • The process of generating and suppyling electricity isn't massively efficient.
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Supplying Electricity Efficiently II

  • Unfortunately most power stations produce a lot of waste energy (eg heat loss to the enviroment) as well as energy we can make use of. Basically the energy in each bit of fuel is broken down into two parts the useful bit and the wasteful bit.
  • TOTAL energy input = USEFUL energy output + WASTE energy output
  • Efficiency = USEFUL energy OUTPUT / TOTAL energy INPUT (X100%)
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Electrical Power I

Running costs depend on an appliance's power rating:

  • Power's measured in watts (W) or kilowatts (kW) - where 1 watt means 1 joule per second. For example, a light bulb with a power rating of 100 W uses 100 J of electrical energy every seconds. And a 2 kW kettle converts electrical energy at the rate of 2000 J per second.
  • If they're both on for the same amount of time, the kettle is much more expensive to run than the bulb, because it consumes more energy.
  • The power rating of an appliance depends on the voltage and the current it uses:
  • power (in W) = voltage (in V) x current (in A)

Kilowatt-hours (kWh) are 'UNITS' of energy:

  • Your electricity meter records how much energy you use in units of kilowatt-hours/ kWh.
  • A kilowatt-hour is the amount of electrical energy converted by a 1kW appliance left on for 1 hour.
  • The higher the power rating of an appliance, and the longer you leave it on, the more energy it consumes and the more it costs:
  • energy supplied (in kWh) = power (in kW) x time (in hours)
  • cost = number of units x price per unity
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Electrical Power II

Off-peak electricity is cheaper:

Electricity supplied during the night (off-peak) is sometimes cheaper. Storage heaters take advantage of this - they heat up at night and then release the heat slowly throughout the day. If you can put washing machines, dishwashers, ect. on at night, so much the better.

ADVANTAGES of using off-peak electricity:

  • Cost-effictive for the electricity company - power stations can't be turned off at night, so it's good if there's a demand for electricity at night.
  • Cheaper for consumers if they buy electricitiy during the off-peak hours.

DISADVANTAGES of using off-peak electricity:

  • There's a slightly increased risk of fire with more appliances going at night but no one watching.
  • You start fitting your routine around the cheap rate hours - ie: you might stop enjoying the use of electricity during the day.
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The Greenhouse Effect I

Some radiation from the Sun passes through the atmosphere:

  • The Earth is surrounded by an atmosphere made up of various gases - the air.
  • The gases in the atmosphere filter out certain types of radiation from the Sun = they absorb or reflect radiation of certain wavelengths (infared).
  • However, some wavelengths of radiation - mainly visable light and some radio waves - pass through the atmosphere quite easily.

The greenhouse effect helps regulate Earth's temperature:

  • The Earth absorbs short wavelength EM radiation from the Sun. This warms the Earth's surface up. The Earth then emits some of this EM radiation back out into space - this tends to cool us down.
  • Most of the radiation emitted from Earth is longer wavelength infrared radiation - heat.
  • A lot of this infrared radiation is absorbed by atmospheric gases, including carbon dioxide, methane and water vapour.
  • These gases then re-radiate heat in all directions, including back towards the Earth.
  • So the atmosphere acts as an insulating layer, stopping the Earth losing all its heat at night.
  • This is known as the 'greenhouse effect'. (In a greenhouse the sun shines in and the glass helps keep some of the heat in). Without the greenhouse gases (CO2, methane, water vapour) in our atmosphere, the Earth would be a lot colder.
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The Greenhouse Effect II

Humans are causing an increase in the amount of greenhouse gases.

Over the last 200 years or so, the concentration of greenhouse gases in the atmosphere has been increased. This is because some of the sources of them are increasing, so more gases are being released.

  • CARBON DIOXIDE:
  • People are using more energy (eg: travel more in cars) - which we get mainly from burning fossil fuels, which releases more carbon dioxide.
  • More land is needed for houses and food and the space is often made by chopping down and burning trees - fewer trees mean less CO2 is absorbed and burning releases more CO2
  • CO2 also comes from natural sources - eg: respiration in animals and plants, and volcanic eruptions can release it.
  • METHANE:
  • Cattle farming has increased to feed the growing population - cattle digestion produces methane, so the amount of methane is increasing.
  • Decaying waste in landfill sites produces methane;the amount of waste is increasing so is methane.
  • Methane is released naturally by volcanoes, wetlands and wild animals.
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The Greenhouse Effect III

  • WATER VAPOUR:
  • Most water vapour comes from natural sources - mainly oceans, seas, rivers and lakes. As global temperature increases, so could the amount of water vapour.
  • Power stations also produce water vapour, which can affect the amount in the local area.
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Global Warming and Climate Change I

Upsetting the greenhouse effect has led to climate change:

  • Since we started burning fossil fuels, the level of carbon dioxide in the atmosphere has increased.
  • The global temperature has also risen during this time (global warming). There's a link between concentration of CO2 and global temperature.
  • A lot of evidence has been collected that shows the rise of CO2 is causing global warming by increasing the greenhouse effect.
  • For example, climate models can be used to explain why the climate is changing now. We know that the Earth's climate varies naturally. But climate modelling over the last few years has shown that natural changes don't explain the current 'global warming' - and that the increase in greenhouse gases due to human activity is the cause.
  • So there's now a scientific consensus (general argreement) that humans are causing global warming.
  • Global warming is a type of climate change. But it also causes other types of climate change, eg: changing weather patterns.
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Global Warming and Climate Change II

Changes to the weather can have human and natural causes:

  • The climate is very complicated - conditions in the atmosphere, oceans and land all affect one another.
  • Changes in the temperature can have large effects on the weather.
  • For example, many regions will suffer more extreme weather because of global warming, eg: longer, hotter droughts.
  • Hurricanes form over warm water - so with more warm water you'd expect more hurricanes
  • Changing weather patterns also affect food production - some regions are now too dry to grow food, some too wet. This will get worse as temperature increases and weather patterns change more.
  • Temperature change, and so changes to the weather, can have both human and natural causes:
  • HUMAN: a) The rising CO2 level caused by humans is affecting the greenhouse effect and causing global warming. b) Soot and gases produced by factories can reflect heat from cities back down to Earth which can cause increases in local temperatures.
  • NATURAL: a) Ash and gases thrown into the atmosphere by volcanoes can reflect radiation from the Sun back into space, causing the Earth to cool down. b) changes in our orbit round the Sun can cause ice ages.
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Nuclear Radiation I

Nuclear radiation causes ionisaton:

  • When an unstable nucleus decays, it gives off one or more kinds of radiation.
  • Radioactive materials give out nuclear radiation over time.
  • The three kinds of radiation are alpha, beta and gamma.
  • All three kinds of radiation can cause ionisation - the radiation causes atoms to lose or gain electrons, turning those atoms into ions.
  • Positive ions are formed when atoms lose electrons.
  • Negative ions are formed when atoms gain electrons.
  • Ionisation can also initiate (start) chemical reactions between different atoms.
  • When radiation enters human cells it can ionise molecules and damage DNA. This can cause mutations in the cell that could lead to cancer.
  • Very high doses of radiation can kill cells completely.
  • The ionising power of each kind of radiation is linked to how far it can penetrate materials. The further the radiation can penetrate before hittin an atom, the less ionising it is.

Alpha particles are big and heavy:

  • Alpha particles are relatively big, heavy and slow moving (they're 2 protons and 2 neutrons)
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Nuclear Radiation II

  • Because of their size they're stopped quickly - they don't penetrate far into materials. Alpha particles can be stopped by paper or skin.
  • This means they're strongly ionising - they bash into loads of atoms and knock  electrons off them.

Beta particles are electrons:

  • Beta particles are just electrons - so they're small and they move quite fast.
  • Beta particles penetrate moderately (further than alpha particles) before colliding, so they're moderately ionising. But they can still be stopped by a thin sheet of metal - a few millimeters of aluminium.

Gamma rays are ver high frequency electromagnetic waves:

  • After spitting out an alpha or beta particle, the nucleus might need to get rid of some extra energy. It does this by emitting a gamma ray - a type of EM radiation 
  • Gamma rays have no mass and no charge. They can penetrate a long way into materials without being stopped - meaning they're weakly ionising (they tend to pass through rather than collide with atoms) But eventually they do hit something and do damage.
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Nuclear Radiation III

  • They can be stopped using very thick concrete or a few centimetres of lead.

You can identify the type of radiation by its penetrating power:

  • You can tell which kind of radiation you're dealing with by what blocks it.
  • eg: place a sheet of paper between the radiation source (some radioactive material) and a detector (a Geiger counter):
  • If no radiation reaches the detector then it must be alpha.
  • If radiation is still reaching the detector then it could be beta or ggamma. Swap the paper for aluminium - if no radion reaches it now, it must be better. But if radioactivity still gets through, it must be gamma.
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