Physics 1.4 JaskiratK

Physics - P1.4

Generating Electricity

Electricity is a convenient source of energy and can be generated in a number of different ways. You will need to weigh up the advantages and disadvantages of other ways of producing energy, such as the use of nuclear power stations.

Coal, oil and natural gas are primary energy sources. Electricity is a secondary energy source because we use primary energy sources to produce it. These primary sources can be non-renewable or renewable. Electricity itself is neither non-renewable nor renewable.

Electricity is convenient because:- It is transmitted easily over distance, through electricity cables.- It can be used in many ways, for example electric lamps, heaters, motors etc.

Process Of Using Electrical Energy:

Electricity

Generating Electricity

Generators are the devices that transfers kinetic energy into electric energy.Turning Generators Directly:

Generators can be turned directly, for example, by:- Wind Turbines - Hydroelectric Turbines - Wave and Tidal TurbinesWhen electricity is generated using wave, wind, tidal or hydroelectric power (HEP) there are two steps:1. The turbine turns a generator.2. Electricity is produced.

Turning Generators Indirectly:Generators can be turned indirectly using fossil or nuclear fuels. The heat from the fuel boils water to make steam, which expands and pushes against the blades of a turbine. The spinning turbine then turns the generator.

These are the steps by which electricity is generated from fossil fuels:

1. Heat is released from fuel and boils the water to make steam.

2. The steam turns the turbine.3. The turbine turns a generator and

electricity is produced.4. The electricity goes to the

transformers to produce the correct voltage.

Physics - P1.4

Energy Sources

Our renewable energy resources will never run out. Their supply is not limited. There are no fuel costs either. And they typically generated far less pollution than fossil fuels.

Renewable Energy Resources Include:- Wind Energy - Water Energy (Wave Machines, Tidal Barrages, Hydroelectric Power)- Geothermal Energy- Solar Energy- Bio-mass Energy (Energy Released From Wood)

Non-Renewable Energy Resources:There is a limited supply of non–renewable energy resources, which will eventually run out. They include:- Fossil Fuels (Coal, Gas and Natural Gas)- Nuclear Fuels (Uranium)

Fossil fuels release carbon dioxide when they burn, which adds to the greenhouse effect and increases global warming. Of the three fossil fuels, coal produces the most carbon dioxide, for a given amount of energy released, while natural gas generates the least.The fuel for nuclear power stations is relatively cheap. But the power stations themselves are expensive to build. It is also very expensive to dismantle old nuclear power stations or store radioactive waste, which is a dangerous health hazard.

Physics - P1.4

Nuclear PowerThe main nuclear fuels are uranium and plutonium, both of which are radioactive metals. Nuclear fuels are not burned to release energy. Instead, heat is released from changes in the nucleus. Just as with power stations burning fossil fuels, the heat energy is used to boil water. The kinetic energy in the expanding steam spins turbines, which drive generators to produce electricity.

Advantages:Unlike fossil fuels, nuclear fuels do not produce carbon dioxide.

Dis-Advantages:Like fossil fuels, nuclear fuels are non-renewable energy resources. And if there is an accident, large amounts of radioactive material could be released into the environment. In addition, nuclear waste remains radioactive and is hazardous to health for thousands of years. It must be stored safely.Nuclear waste is given different categories.

Category: Examples: Disposal:

Low Level Contaminated equipment, materials and protective clothing.

They are put in drums and surrounded by concrete, and put into clay lined landfill sites.

Intermediate Level

Components from nuclear reactors, radioactive sources used in medicine or research.

They are mixed with concrete, then put in a stainless steel drum in a purpose-built store.

High Level Used nuclear fuel and chemicals from reprocessing fuels.

They are stored underwater in large pools for 20 years, then placed in storage casks in purpose-

built underground store where air can circulate to remove the heat produced. High level waste

decays into intermediate level waste over many thousands of years.

Physics - P1.4

Nuclear Power StationsThe main nuclear fuels are uranium and plutonium. In a nuclear power station nuclear fuel undergoes a controlled chain reaction in the reactor to produce heat - nuclear to heat energy.

- Heat is used to change water in the boiler into steam.

- The steam drives the turbine. = Heat to Kinetic Energy.

- This drives the generator to produce the electricity. = Kinetic to Electrical Energy.

Advantages:Unlike fossil fuels, nuclear fuels do not produce carbon dioxide or sulphur dioxide. 1 kg of nuclear fuel produces millions of times more energy than 1 kg of coal.

Dis-Advantages:- Like fossil fuels, nuclear fuels are non-

renewable energy resources.- If there is an accident, large amounts of

radioactive material could be released into the environment. Although modern reactor designs are extremely safe.

- Nuclear waste remains radioactive and is hazardous to health for thousands of years. It must be stored safely.

This waste material can never be used to make a 'nuclear bomb' which is sometimes mooted as a negative aspect of nuclear power stations. It is the fission fragments from a nuclear chain reaction and

not fissionable itself.

Physics - P1.4

Nuclear FissionNuclear power stations use the heat released by nuclear reactions to boil water to make steamThe type of nuclear reaction used is called nuclear fission. In nuclear fission:1. A neutron collides with a uranium nucleus. A uranium nucleus is large and unstable.2. The uranium nucleus splits into two similar-sized smaller nuclei.3.More neutrons are released.4. These neutrons can then collide with more uranium nuclei.These processes are repeated continuously, forming a chain reaction.

Rate Of Energy Released:In a nuclear reactor, the reaction is controlled so that energy is released at a steady rate.The energy released in nuclear fission is far greater than the energy released in a chemical reaction, such as burning fuel. This means that the power output of a nuclear power station is large. The lifetime of a nuclear power station is about 20 years.

Advantages & Dis-Advantages:In considering the subject of nuclear power, it is important to weigh up the advantages and the disadvantages. These are some of the advantages:- No carbon dioxide is produced when the station is operating.- There is a high power output.- A small amount of fuel is needed, when compared with coal or gas.There are some dis-advantages:- Hazardous radioactive waste Is produced.- Building the power station is quite expensive.- Decomposing the power station at the end of their lifetime is very costly.

The nuclear fuel, usually uranium oxide, is held in metal containers called fuel rods. These are lowered into the reactor core. A coolant, usually water or carbon dioxide, is circulated through the reactor core to remove the heat. Control rods are also lowered into the core. These absorb neutrons and control the rate of the chain reaction. They are raised to speed it up, or lowered to slow it down.

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Outline Of A Nuclear Reactor:Physics - P1.4

Power Stations

Thermal Power StationIn a thermal power station fuel such as coal, oil or gas is burned in a furnace to produce heat - chemical to heat energy.- This heat is used to change water into

steam in the boiler.- The steam drives the turbine. = Heat to

Kinetic Energy.- This drives the generator to produce the

electricity. = Kinetic to Electrical Energy.

Efficiency Of Power StationsThe energy produced by burning fuel is transferred as heat and stored in water as steam. The energy in steam is transferred to movement in a turbine, then to electrical energy in the turbine. Energy is lost to the environment at each stage. Here is a Sankey diagram to show these losses.

Only about a third of the energy stored in the fuel was transferred as electrical energy to customers.

Physics - P1.4

Hydro-Electric Power StationsIn a hydroelectric power station water is stored behind a dam in a reservoir. This water has gravitational potential energy. - The water runs down pipes (potential to kinetic energy) to turn the turbine.- The turbine is connected to a generator to produce electricity. (kinetic to electrical energy).

At pumped storage hydroelectric stations water is pumped back

into the reservoir when there are periods of low power demand.

This is often when there is excess energy being produced by other

power stations.This stores energy and during

higher demand periods the water can be allowed to flow back down

to produce electricity just like a normal power station. Such a system saves energy and also

can be turned on quickly at times of peak demand.

Physics - P1.4

Power StationsPower stations which burn fossil fuels to produce electricity are one of the main contributors of carbon dioxide in the air.One way to reduce the air pollution caused by power stations is to use less electricity. Some ways to do this are:- Turning down the heating at home.- Insulating your home.- Turning lights off when leaving a room.- Using low-energy lamps.- Using a microwave instead of a electric oven.- Not leaving TV’s on standby.

Sulfur Dioxide:Power stations give out sulfur dioxide which is a cause of acid rain. The amount of sulfur dioxide given off by a power station can be reduced by:removing sulfur from natural gas and fuel oilremoving sulfur dioxide from the flue gases emitted by coal-burning power stationsCoal-powered stations give off solid particulates. These can also be removed from the flue gases.

Physics - P1.4

Scientific applications give people things that they value, but may have undesirable impacts on the environment.• Our society uses more and more energy every year, but the carbon dioxide produced by most

power stations is believed to be causing serious damage to the climate.Natural resources should be used in a sustainable way.• The use of renewable energy sources would guarantee energy for the future. At the moment,

renewable energy sources cannot provide enough energy.There are official regulations and laws which control scientific research and applications.• The nuclear industry is regularly inspected to ensure that standards of safety are maintained.Some applications of science have ethical implications. One point of view is that the right decision is the one which gives the best outcome for most people. Another point of view is that certain actions are never justified because they are wrong.Disposal of nuclear waste raises ethical problems:• Some people say that we must have nuclear power, or we will not be able to combat global

warming and still produce enough energy.• Others say that it is unethical to produce waste that will still be dangerous in many thousands of

years’ time.Weighing Up The Arguments:

Before deciding on a course of action, it is important to ask if it is feasible. Can it be done? Then it is possible to consider if it ought to done.• If nuclear waste could be sent down into the Earth’s mantle, it would take millions of years to

resurface. Unfortunately, there doesn’t seem to be any way to do this. It is not feasible.• Nuclear waste could be sent into space in rockets so that it falls harmlessly into the Sun.

Unfortunately, this would be far too expensive, and any accident on take-off would spread dangerous waste over a large area. It ought not to be done.

In different social and economic contexts, different decisions might be taken.• Many developing countries insist that they need to burn fossil fuels in their power stations, even if it

produces global warming. They need this to allow them to catch up with the standard of living that we enjoy.

Ideas About SciencePhysics - P1.4

National GridElectricity is distributed from power stations to consumers through the National Grid, which allows distant power stations to be used. It also allows a mix of different energy resources to be used efficiently to supply the country’s electricity, whatever the local demand.

Transformers:Electricity is transferred from power stations to consumers through the wires and cables of the National Grid. When a current flows through a wire some energy is lost as heat. The higher the current, the more heat is lost. To reduce these losses, the National Grid transmits electricity at a low current. This needs a high voltage.Transformers are used in the National Grid. A transformer is an electrical device that changes the voltage of an alternating current (ac) supply, such as the mains electrical supply. A transformer that:• Increases Voltage – Step-Up Transformer• Decreases Voltage – Step-Down Transformer

Power stations produce electricity at 25,000 V. Step-up transformers change the voltage to the very values needed to transmit electricity through the National Grid power lines. Electricity is sent through these at 400,000 V, 275,000 V or 132,000 V. This reduces energy losses during transmission but the voltages would be dangerous in homes. Step-down transformers are used locally to reduce the voltage to safe levels. The voltage of household electricity is about 230 V.

Main Features:Electricity from a power station goes to:1.Step-Up Transformers2. High Voltage Transmissions Lines.3. Step-Down Transformers4. Consumers – Homes, Factories, Shops.

Advantages:- The main advantage is that they are easier to

repair if damaged. (Usually just go up a ladder and do the necessary work).

- They are not restricted by the landscape that they are in e.g. you can easily suspend them over a

motorway or river.- Also they have a less chance of electrocuting

people as they are so high up.- Lose less energy then if they were underground as they do not have any good conductors near them to

transfer energy away as easily.- Cheaper to set up and maintain than if they were

underground. 

Over Head Power LinesDis-Advantages:

- Main problem is that they visually pollute the areas they set up in.

- Suffers from problems like vandalism, assisting terrorism (Easy Access), and lightning strikes.

- Birds are low lying aircrafts can sometimes fly into them.

Under Ground Cables

Advantages:- Not visibly blight.

- Not easily damaged by elements.- Away from animals and humans.- Cannot be damaged by weather.

- Not a risk to aircrafts.

Dis-Advantages:- Extremely expensive, as they need to be

insulated from the ground and other neighbouring cables.

- Trenches must be dug to be repaired and installed.

- Could be damaged by people digging.(E.G Builders, Ordinary People).

- Cables are more expensive per foot.