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Static And Current ElectricityWhat is Static Electricity?Rubbing a polythene strip on wool causes some of the outer electrons in the wool to move over to the polythene strip. As the polythene gains electrons it becomes negatively charged. The wool looses electrons and is left with a net positive charge (more protons to electrons).Static electricity is caused by the transfer of charge.Atoms are made up of protons, neutrons and electrons each with their own properties.Protonshave aPositive(+) charge.Electronshave aNegative(-) charge.NeutronsareNeutral(no charge).The positive charges (protons) are held in the nucleus of the atom.The negative charges (electrons) are spread in orbits around the nucleus.The protons and neutrons are held very tightly in the nucleus. But some of the electrons are held very loosely and can move from one atom to another. If an atom looses an electron the number of protons (positive charges) exceeds the number of electrons (negative charges) and the atom is positively charged.If an atom gains an electron the number of protons (positive charges) is lesser than the number of electrons (negative charges) and the atom is negatively charged.One method in which electrons can be moved or transferred is by rubbing two insulators together. Rubbing causes friction between the two surfaces increasing the surface contact and allowing more electrons to be transferred. The object which looses electrons becomes positively charged and the one that gains the electrons becomes negatively charged.Therefore,Static Electricity is the imbalance of Positive and Negative Charge

Attraction & RepulsionRubbing a polythene strip on wool causes some of the outer electrons in the wool to move over to the polythene strip. As the polythene gains electrons it becomes negatively charged. The wool looses electrons and is left with a net positive charge (more protons to electrons).Only the negative electrons move. The positive protons remained fixed in the atoms nucleus.Rubbing materials to generate charge only works for insulated objects. Conductors direct the charge flow to earth.When two electrically charged bodies are brought together they exert a force on each other. Electrically charged objects may attract or repel each other or attract small uncharged objects place near them.

Example : BalloonA balloon can be made to stick to a wall by using the principles of electrostatics.When a balloon is rubbed against clothes the negative electrons from the clothes get transferred to the balloon making the balloon negatively charged. When the balloon is placed near a wall or ceiling (a neutral object) it stays there and doesnt fall. This is because the negative charge of the balloon repels some of the electrons in the wall or ceiling away from the surface. This results in an overall positively charged surface causing the negatively charged balloon to be attracted (remember opposite charges attract).The separated charges in the wall or ceiling are calledINDUCEDcharges.

Static HazardsSparksSparks can cause explosions. When flammable liquids like gasoline (petrol) are transferred from tankers to aircrafts static electricity poses a very serious hazard. Gasoline is an insulator. When it transferred from a tanker to an aircraft it rubs against the inside of the hose and builds up a lot of charge. This large amount of charge can form sparks and cause an explosion.To prevent this from happening tankers/aircrafts use grounding or earthing devices. These are copper wires on the hose and the aircraft that draw the electrical charge away from the gasoline and into the ground/earth (hence the name grounding or earthing).

LightningIn storm clouds water droplets collide with dust particles, ionising radiations and each other. These collisions cause electrons to be knocked of the particles and accumulate in the cloud. The negative charges collect at the bottom of cloud and induce positive charges to accumulate on the ground. Eventually, the potential difference between the cloud and the ground become so great that the negative charges from the cloud are attracted towards the positive charges from the ground. When the two charges meet a flash of lightning is produced. Lightning bolts can heat up the air to temperatures hotter than the sun this causes the air around the bolt to expand explosively producing the sound we hear as thunder. As lLightning HazardsLightning strikes are hazardous to buildings especially tall ones like tower blocks and chimney stacks. The energy in a bolt of lightning can severely damage and burn buildings. Lightning conductors provide protection for building by providing the path of least resistance for the lightning into the earth.Lightning conductors are a sharp pointed metal rod placed on the top of a building. As charged storm clouds induce positive charge the point of the lightning conductor becomes positively charged. If lightning strikes it will be hit the conductor (due to it being the tallest object with the positive charge), it will the travel down the rod and into earth where it will be dissipated safely.

light travels a million times faster than sound we see the lightning before we hear the thunder.

Conductors & InsulatorsConductorsare materials which allow the electrons to move freely inside them. All metals are good conductors because they contain a large number of free electrons inside them that can move easily from atom to atom.Insulatorsdo not allow electrons to pass through them. They do not contain free electrons inside them.ConductorsInsulators

All metals e.g. copper, silver, etc.Glass

WaterPlastics

SkinAir

Rubber

Uses of Static Electricity

1. The electrostatic precipitatorElectrostatic precipitators are used in industry for environmental protection. In factories, power plants and chemical plants smoke and other exhaust have to be treated to remove dust particles and other particulates before it is released into the atmosphere.Highly positively charged wires are stretched across the centre of the chimney or exhaust vent to form a grid. The wires are charged to a positive charge of about 50,000V. As the smoke passes over the wires the particles carried in the smoke become positively charged. These particles are then attracted towards negatively charged collecting plates where they stick. Thus, the dust particles are separated from the smoke which then carries on up the chimney and into the atmosphere. The negatively charged collecting plates are periodically struck with a mechanical hammer to remove the dust particles which then drop into a collecting bin.Remember, the principle would also be true if the wires were negatively charged and the collecting plates positively charged. As the process relies on the principle that opposite charges attract.2. Paint Spraying/Crop SprayingThe principles of electrostatics are used are used by industry in the process of paint spraying for e.g. the automotive industry when spraying cars. The nozzle of the spray gun is given a charge. The paint droplets exiting the nozzle gain this charge. As the droplets all hold the same charge they repel each other so that they spread out into a fine mist. The object to be painted is grounded or earthed. The charged droplets are attracted to the grounded object, even the back of it due to the electrostatic attraction (remember charged objects are attracted to uncharged objects). This process requires less paint and gives a uniform finish.The same principle is used to benefit farmers in crop spraying. If the fertilizer/pesticide is given the same charge the droplets repel to form a larger cloud thereby increasing the coverage. These are then attracted to the uncharged crops.3. The PhotocopierPhotocopiers consist of a drum or belt covered with a layer of photoconductive material. A photoconductive material conducts electricity when struck by light (photomeaning light andconductivereferring to conducting electrons).When a photocopier is started a high voltage wire distributes a positive charge evenly on the surface of the belt or drum. An intense beam of light moves across the sheet of paper to be copied placed on the glass surface. The dark areas on the paper absorb the light and the white areas reflect the light back onto the drum/belt below. The reflected light strikes the positively charged photoconductive material on the metal neutralising it (by producing electrons). The dark areas on the paper for e.g. the text or picture that do not reflect the light leave regions of positive charges on the surface of the belt/drum (like a shadow).Negatively charged, dry black pigment particles known as toner are then spread over the drum/belt. These negatively charged particles are attracted to the positively charged regions on the drum/belt (remember opposite charges attract). A blank sheet of paper is passed over the charged wire making it positive and then passed over the drum/belt. The positively charged paper attracts the toner off the drum/belt. The paper plus toner is then heated and passed through rollers to melt and fuse the toner to the paper.

Electric CurrentSimply defined, electric current is a flow of electrons.As, electrons are negatively charged, it can be further added that electric current is the flow of negative charge.

In order for an electric current to flow there needs to be complete circuit with no gaps. A basic electric circuit consists of a metallic wire connected to an electrical cell and an electrical component such as a lamp. The metallic wire contains a large number of free electrons that can move easily from atom to atom, it is the movement of these free electrons that give rise to the current.When the switch is in the off position there is a gap in the circuit and the electrical current cannot flow. In the on position the switch completes the circuit allowing current to flow and thereby lighting the lamp.Electric current is measured in units called Amperes (amps for short) and has the symbol A.

1 ampere is a set number of electrons flowing through each point of an electrical circuit per second. 1 ampere is approximately 6 million million million (6 x 1018) electrons per second flowing past each point. As the charge on electrons is tiny the unit of charge used is the coulomb (C). 1 coulomb is equal to the charge on 6 million million million (6 x 1018) electrons. Therefore when a current in a circuit is 1 ampere the flow of charge is 1 coulomb per second.Electric current is measured by an Ammeter.

By connecting an ammeter in series in an electrical circuit the size of the electrical current can be measured.It is important to remember that as an electrical current flows through a component such as a lamp or ammeter it is not used up but flows in a continuous loop. The battery supplies the energy source for the electrons to move. These transfer or loose energy when passing through components such as lamps in the form of heat and light but do not get used up themselves. Therefore in series circuit the electrical current is the same in all parts of the circuit.

Potential DifferenceIn an electrical circuit the cell (or battery) pushes the electrons around the circuit. It does this by transferring chemical energy from the materials in the cell to electrical potential energy to the electrons.When electrons pass through a lamp in the circuit they give up (lose) some of the electrical potential energy to the thin wires in the lamp in the form of heat and light. Therefore across the lamp there is an electrical energy difference. The electrons entering the lamp have a higher electrical energy than the electrons leaving the lamp. This difference in electrical potential energy across the lamp is called a POTENTIAL DIFFERENCEorp.d.Potential difference is measured in units called Volts and has the symbol VIt is for this reason potential difference is sometimes also referred to as voltage.Potential difference is measured by a Voltmeter.

By connecting a voltmeter in parallel across the component of interest the potential difference across it can be measured (in this case the lamp)

ResistanceElectric current is the flow of electrons. As these electrons flow around a circuit they bump into the atoms in the conducting wire and electrical components. These constant collisions make it difficult for the current to flow or in other words resist the electrical current.Therefore,Resistance is the property of an object or substance of resisting or opposing the flow of electrical current.Resistance is measured in units called Ohmsand has the symbol

Conventional Current & Electron FlowElectric current is the flow of electrons from the negative terminal to the positive terminal of a cell. This is because electrons are negatively charged and want to move away from the negative terminal and head towards the positive terminal.When cells were first invented the theory of electron flow mentioned above was unknown. Rather it was incorrectly assumed that the movement was from the positive to negative terminal. Therefore, circuit diagrams showed the current moving from the positive terminal to the negative terminal. We have unfortunately stuck with this convention to this day and so current flow from positive to negative is called,conventional current flowand is used when drawing circuit diagrams.Series and Parallel CircuitsElectrical components can be arranged in a circuit either in series or parallel.

Series CircuitsFor components connected in series the following rules apply:1. Electric CurrentThe electrical current through each component is the same,as all the current has to flow through everything in the circuit.

2. Potential DifferenceThe potential difference across each component adds up to the potential difference across the battery.This is because the energy transferred from the battery to the electrons must equal the amount of energy transferred by the electrons to the components. The potential difference provided by cells connected in series is the sum of the potential difference of each cell.

3. ResistanceThe total resistance across the components in series is equal to the sum of each resistance across the components.The potential difference is largest across the component with the greatest resistance as more energy is transferred by the electrons to overcome the resistance.

Parallel CircuitsFor components connected in parallel the following rules apply.1. Electric CurrentThe total current through the whole circuit is the sum of the current through each electrical component.The current in a parallel circuit branches out after leaving the battery and recombines before entering back in.

2. Potential DifferenceThe potential difference across each component is the same.

3. ResistanceThe combined resistance across the components in parallel is less than either of the separate resistance across the components.

Circuit SymbolsCircuit diagrams are used to show how electrical components are connected together. Each electrical component has its own symbol. In order to draw basic circuit symbols it is important you learn the following symbols.Component Symbol Function

Wire

Made from a metallic conductor so current can easily pass from one part of the circuit to anotherSwitch (open)

On/Off switch in open position the circuit is broken so no current flowsSwitch (closed)

On/Off switch in closed position the circuit is complete and current flowsCell

Supplies the electrical energy to the circuit the larger terminal on the left is the positive (+) terminalBattery

A battery is more than one cell.Lamp

Coverts electrical energy to light.Fuse

A safety device which melts to break the circuit if the electrical current flowing through it exceeds a specified value.Voltmeter

Instrument used to measure potential difference.Ammeter

Instrument used to measure electrical currentResistor

Restricts the flow of electrical current can be used to limit the flow of current to a particular componentDiode

A device which only allows current to flow in one directionThermistor

Converts heat to electrical resistanceVariable resistor

Used to control currentLight dependant resistor

Converts light to electrical resistanceElectrical Circuits

Ohms LawOhms Law is the named after the German scientist Georg Ohm who in the 1820s conducted experiments investigating the relationship between potential difference and current on various lengths and types of metal conductors.The findings of his experiments led to Ohms Law which states:The current flowing through a metallic conductor held at constant temperature is directly proportional to the potential difference between the endsIn other words, if the current doubles the potential difference doubles or if the current triples the potential difference triples.Ohms Law can also be stated for the current through a resistor as:The current flowing through a resistor held at constant temperature is directly proportional to the potential difference across the resistorThe relationship between potential difference, current and resistance is given by the equation:Potential Difference or Voltage (V)= Current (I) x Resistance (R)

V = I x RTipLearn this equation and practice questions requiring the use of this equation.

Current Potential Difference GraphsCurrent potential difference graphs are used to show how the current through a component varies with the potential difference across it.Current Potential Difference Graph for a resistor at constant temperature

Current Potential Difference graph for a Filament Lamp

Current Potential Difference graph for a Diode

Current Potential Difference graph for a Thermistor

Current Potential Difference graph for a Light Dependant Resistor (LDR)

Using the Equation: V = I x RA simple way of using the Ohms Law relationship is to use the triangle method. This involves taking the equation in the form where there is only multiplication and no division. In the case of Ohms Law in the form V = I x R and arranging it in a triangle so that V is at the top and I and R at the bottom.

ExampleIn the circuit below the voltmeter reading across the lamp is 3V and the ammeter reads 2A of electrical current. What is the resistance across the lamp?

Potential Difference across the lamp = V = 3VElectrical current through the lamp = I = 2AElectrical resistance across the lamp = R = ?

Using V = I x R

Require resistance therefore cover R in the triangle.

Thus,R = V / IR = 3 / 2 = 1.5Diodes, LDRs and ThermistorsThe DiodeA diode allows a current to flow through it in one direction only.It has the symbol:

Remember circuit diagrams are drawn inconventional current. So the arrow on the diode symbol indicates the direction in which the conventional current can flow. When the arrow of the diode is in the same direction as the conventional current flow it is said to be forward biased and current flows.

When the arrow of the diode is in the opposite direction to the conventional current flow it is said to be reversed biased and no current flows.Diodes are used in electric circuits to protect electrical equipment. In electrical equipment such as radio or computers damage can be caused if the battery is connected the wrong way round. A diode in the circuit only allows the current to pass through when the battery is connected correctly. If the battery is connected the wrong way round no current passes through the diode and the electrical circuit for the equipment is protected from damage.

Current Potential Difference graph for a Diode

The Light-Dependent Resistor (LDR)In a light-dependent resistor the resistance decreases as the light intensity (brightness of light) increases.It has the symbol:

At low light levels or in the dark the resistance of an LDR is high and little current flows through it.

In bright light the resistance of an LDR is low and more current flows through it.The properties of an LDR are put to use in digital camera. The shutter speed of a camera can be controlled by an LDR. If light levels are low changes in the resistance of the LDR can be measured causing the shutter to stay open for longer. An LDR can also be used in a burglar alarm circuit for e.g. inside a safe. When the safe is closed it is dark and so the resistance of the LDR is high. If it is opened and the LDR exposed to light the resistance drops allowing current to flow which can then trigger a relay circuit which rings an alarm.Current Potential graph for a Light - Dependent Resistor (LDR)

The ThermistorA thermistor is an electrical component in which the resistance decreases as the temperature increases.It has the following symbol:

At low temperature the thermistor has a high resistance and little current can flow through it.

But at high temperatures the resistance of the thermistor is low and more current flows through it.It is this property of the thermistor that allows it to be used as a temperature sensor. A Thermistor can be used as an electronic thermometer in which the current flowing through it at different temperatures can be calibrated in degrees Celsius to give a temperature reading. A thermistor is also used in a fire alarm. A thermistor is placed into a fire alarm circuit such that above a set temperature the current through the thermistor is at an amount to trigger a relay circuit which rings an alarm.Current Potential graph for a Thermistor

Direct Current (dc) & Alternating Current (ac)Direct Current (dc)This is the continuous flow of electrons through a conducting material such as a metal wire.In direct current the electron flow is always in the same direction.Alternating Current (ac)An alternating current is one which is constantly changing direction or alternates in direction.The back and forth motion occurs between 50 and 60 times per second, depending on the electrical system of the country.Therefore, the difference between dc and ac is that dc is continuous and in one direction, whereas ac alternates in directionCells and BatteriesCells and batteries supply current which always passes in the same direction and are thus sources of direct current.The underlying principle of operation in a battery is anELECTROCHEMICAL REACTIONi.e. a chemical reaction that produces electrons. In a battery electrons are made to move inone directionby lining up different types of metals/materials. The principle behind the selection of metal is to choose one with a lot of free electrons and the other requiring free electrons. The electrons are produced by the chemical reaction between the electrolyte and metal.Below is an explanation of the battery reaction:The Sulphuric Acid reacts with the Zinc electrode. As a result the acid molecule breaks up into2H+and oneSO42-ions.The Zinc atoms on the surface of the Zinc rod go toZn ------------------------------> Zn2++ 2e-TheZn2+combines with theSO42-Zn2++ SO42-----------------> ZnSO4which dissolves in the acid.The excess electrons flow through the wire and load to the Carbon electrode as this is the easier route.The electrons combine with the hydrogen on the carbon rod releasing hydrogen gas.2H++ 2e----------------------> H2gasThe above only happens when the circuit is complete

Solar CellsSolar cells are also known as photovoltaic cells as they transfer energy from light photons (sunlight) to electrical energy.Mains ElectricityMains electricity is the term used to refer to the electricity supply from power stations to households.Mains electricity is supplied as alternating current (a.c.)Alternating current a.c. is one which is constantly changing i.e. the current flows in one direction and then in the opposite direction, again and again (continuously). In the UK, a.c. supply goes in one direction and then in the opposite direction 50 times in one second.Therefore,the frequency of a.c. supply is 50 cycles per second or 50 hertz.UK mains voltage is 230 Volts.Why a.c.?Alternating current can easily be converted to higher and lower voltages by a transformer. By transporting the electrical energy from a power station at a high voltage and low current is more efficient as if a high current and low voltage was to be used most of the energy would be wasted as heat due to the resistance in the power lines. Converting d.c. to the high voltage low current form is very difficult and cannot be done efficiently.Mains electricity generated from power stations is supplied to UK households via theNational Grid.

Mains electricity (electricity from the power station) enters the house via the Live wire. The live wire carries the incoming electricity and is therefore at 230V and so very dangerous. Mains voltage is more than enough to kill somebody.The neutral wire is also supplied from the power station and is used to complete the circuit. it is earthed back to the power station. Therefore once the electricity from the live wire has given its energy to the appliances in the household the current travels back out of the house via the neutral wire hence the neutral wire has a lower voltage than the live wire.The earth wire is used for safety purposes and carries the current away when there is a fault.

FusesA fuse is an electrical component which is placed in an electrical circuit for protection against electrical faults such as a current surge.A fuse is an electrical wire which is thick enough to allow the required current for the device to pass through it, but thin enough to melt and break the circuit if too much current flows.

The Earth WireElectrical appliances with metal cases usually contain an earth wire. If there is a fault in the appliance and the live wire makes contact with the metal casing, a large current flows from the live wire to the earth wire. This larger current melts the fuse in the live wire breaking the circuit and isolating the appliance from the live wire.The earth wire and the fuse together protect the user and the appliance.Some appliances are double-insulated this means they have a plastic insulating case and therefore do not require an earth wire connect to them. Double-insulated appliance such as hair dryers are marked with the symbol:

Circuit BreakersFuses work on the principal of a large current melting the fuse wire. In some cases faults can occur in which the current may not be large enough to melt the fuse but enough to seriously harm the user of the electrical appliance. For protection against faults of this nature a circuit-breaker is used in place of a fuse.Circuit-breakers offer the following advantages compared to fuses. Circuit-breakers respond quicker than fuses. Circuit-breakers are more reliable. Circuit-breakers are more sensitive. Unlike fuses which only operate once and need to be replaced a circuit-breaker can be reset.There are two main types of circuit-breakers.1. Miniature Circuit Breaker (MCB)2. Residual Current Circuit Breaker (RCCB)1. Miniature Circuit Breaker (MCB)Many different designs and mechanisms are available for this type of circuit-breaker, below are a few examples.Magnetic TypeThis type of MCB consists of an electromagnet. If the current exceeds the rating of the circuit-breaker the pulling force of the magnet attracts an iron latch which breaks the electrical contacts.Thermal TypeThis type makes use of the heating effect of electricity on a bi-metallic strip. An increase in current causes the bi-metallic strip to bend which breaks contact made via a latch mechanism.2. Residual Current Circuit Breaker (RCCB)Residual current circuit breakers work by comparing the current entering the appliance via the live wire with the current leaving the appliance through the neutral wire.The live wire and the neutral wire are wound around iron cores in opposite directions. When the appliance is working correctly all the electrical current entering the appliance via the live wire leaves the appliance through the neutral wire and the magnetic fields generated around the iron cores cancel out. In the event of a fault some of the electric current will flow through the earth wire or in the absence of earthing through the body of the user. This results in an imbalance between the current entering the appliance through the live wire and the current exiting through the neutral wire. This difference in electrical current is called theresidual current.This difference means the decreased electrical current in the neutral wire has a weaker magnetic field associated it to it than the live wire. The two magnetic fields do not balance out and the iron pivot is attracted to the live wire and the contacts are disconnected breaking the circuit.Residual Current Circuit Breakers have the advantage of being highly sensitive and a very quick response time making them safe.The Three Pin PlugIt is important to know how to wire a 3 pin plug correctly. 3 pin plugs are designed so that mains electricity can be supplied to electrical appliances safely.A 3 pin plug consists of three pins (hence the name). Each pin must be correctly connected to the three wires in the electrical cable. Each wire has its own specified colour so as it can be easily identified.The LIVE wire is BROWN.This is connected to a fuse on the live pin. The electric current uses the live wire as its route in.The NEUTRAL wire is BLUE.This is the route the electric current takes when it exits an appliance; it is for this reason the neutral wire has a voltage close to zero.The EARTH wire is GREEN & YELLOWand connected to the earth pin. This is used when the appliance has a metal casing to take any current away if the live wire comes in contact with the casing.Electrical PowerElectrical appliances transform energy. The power of an electrical appliance is the rate at which it transforms energy.Power is defined as the rate of energy transfer. It is measured in watts (W) with 1 watt being equal to 1 joule per second.

ExampleAn electric heater connected to the 230V mains supply draws a current of 4A. Calculate the power of the electric heater?Potential Difference = V = 230VCurrent = I = 4APower = P = ?

Using P = V x I

P = 230 x 4 = 920W

Most electrical appliances have their power and the potential difference of the connecting supply printed on them. With this information we can calculate the required current and the rating of the fuse required.Example Fuse RatingAn electric kettle has a 2500W on a 230V main supply. What fuse should be fitted in the plug?Power = P = 2500WPotential Difference = V = 230VCurrent = I = ?

Using P = V x I triangle,

We require I so cover I on the triangle which gives

Thus,I = P / VI = 2500 / 230 = 10.87A

Therefore a 13A fuse should be fitted.Remember: Fuse values are only available in 3A, 5A and 13A valuesThe energy transferred by an electrical appliance can be determined from the relationshipEnergy transferred(joules, J)= Power(watts, W) xTime(seconds, s)Therefore, if an electric bulb with a power of 60W is on for 10 minutes the energy transferred as heat and light can be calculated as follows:Power = P = 60WTime = t = 10 mins = 10 x 60 = 600s

Energy transferred = 60 x 600 = 36000J = 36kJ

The Electricity BillKilowatt-hours (kWh) is the unit of energy used when calculating the cost of electricity. It is calculated using the equation;Energy transferred(kilowatt hour, kWh)=Power(kilowatts, kW) xTime(hours, h)Remember a kilowatt is 1000 watts (kilo = 1000)Example Cost of using an electric ironA 1500W electric iron is used for 30 minutes. What is the cost of electricity if the unit price is 9.5p per kW h?Power of electric iron = P = 1500W = 1500/1000 = 1.5kWTime = t = 30min = 30/60 = 0.5 h

Energy transferred = power x time = 1.5 x 0.5 = 0.75 kW h

Cost = 0.75 x 9.5 = 7.125pExample Cost from electricity billCalculate the units used and the cost from the electricity bill below?

Units used = current reading previous reading = 8459 7711 = 748Cost = units used x unit price = 748 x 9.2 = 6881.6p

Divide the cost by 100 to convert to pounds = 6881.6/100 = 68.816 = 68.82Energy SourcesElectricity generation involves the transfer of energy from one form to another. The energy sources used in the generation of energy can be classified as two types.1. Non renewable energy source2. Renewable energy sourceNon renewable energy sourcesNon renewable energy is the name given to energy sources which once used cannot be replaced. Examples of non renewable energy resources arefossil fuels and nuclear fuels.Fossil FuelsFossil fuels such as coal, oil and gas get there name because they are formed from the fossilized remains of dead plants and animals.The generally accepted theory is that fossil fuels were formed many millions of years ago by geological processes acting on dead animals and plants (exposure to heat and pressure from the Earths crust).These fuels take many millions of years to form and are currently being depleted (used up) much faster than new ones are being formed.Nuclear FuelsThese are radioactive elements which undergo nuclear reactions (fission) in nuclear reactors generating nuclear energy which in turn is used to generate electricity.Nuclear fuels such as Uranium or Plutonium are mined from the Earths crust. These are of limited supply and cannot be replaced therefore once used are gone forever.The table below is a summary of non renewable energy resources:Petroleum (Oil)

Source:Petroleum is a fossil fuel formed by heat and pressure from the Earths crust acting on the fossilised remains of dead animals and plants. Petroleum reserves exist in the Earths crust sandwiched between layers of impermeable rocks and porous rocks. The petroleum is extracted from these reservoirs drilling oil wells and sinking pipes into the reservoirs to pump the petroleum out.Advantages: Easily converted to energy. Relatively easy to extract. Can be easily transported (pipelines, super-tankers)Disadvantages: Products of combustion (the gases given off when burnt) are atmospheric pollutants and greenhouse gases. Accidents during transport, extraction and refining cause major environmental pollution.Natural Gas

Source:Natural gas is a fossil fuel. Its formation is similar to that for petroleum; however the conversion of the fossilized remains of the dead plants and animals to gas occurs at deeper depths in the Earths crust where the pressure and heat is greater. Natural gas is extracted in a similar way to petroleum by drilling holes and sinking pipes into the gas reservoirs, the gas travels to its surface under its own pressure.Advantages: Relatively easy to extract. Requires little processing (is extracted in a ready to use form) Is the cleanest of the fossil fuels.Disadvantages: Produces greenhouse gases and atmospheric pollutants when burnt.Coal

Source:Coal is a fossil fuel. Coal is formed from the fossilized remains of plants that once grew on the earth. The action of the pressure and heat of the Earths crust over millions of years converts the fossilised remains of these plants into coal. Coal is mined from coal seams in the Earths crust. Where the coal is near the surface of the Earth, open cast mining is used but in areas where the seam is deep underground mining is used to extract the coal.Advantages: Of all the fossil fuels coal has the largest reserves. It is relatively easy and inexpensive to extract.Disadvantages: Open cast mining damages the landscape and ecosystems. The burning of coal produces gases that are atmospheric pollutant and greenhouse gases. Due to the large amount of greenhouse gases coal produces power station require expensive pollution control measures.Nuclear

Source:The most common form of nuclear fuel is Uranium. Uranium is a common metal found in rocks all over the world. However, the particular form of Uranium best suited as a nuclear fuel is Uranium 235 and this is very rare. Uranium 235 is extracted via mining and then processed to make it usable as a fuel.Advantages: Small amounts of fuel produce a large amount of energy. Does not produce atmospheric pollutants and greenhouse gases. Produces small amounts of waste.Disadvantages: Although small amounts of waste are produced, the waste is very dangerous. The waste needs to be disposed of carefully and responsibly. The risk of a nuclear accident can have catastrophic consequences as was the case of Chernobyl.Renewable energy sourcesThese are energy sources that are unlimited (will never run out) and once used are rapidly replenished (continuously replaced).Examples of renewable energy sources are wind, water, geothermal and solar.The table below is a summary of non renewable energy resources:Solar

Source:This is energy from sunlight. Sunlight can be captured by solar panels and its energy transferred to electricity. Energy from the sun can also be focussed onto pipes carrying water transferring heat energy.Advantages: Free unlimited source of energy No waste or greenhouse gases produced.Disadvantages: Source not available at night. Can be an unreliable source of energy unless in a country with a hot climate.Wind

Source:Wind is created by the action of warm air rising and cold air blowing to fill the void created. Hence, the source is the sun as it is its energy that warms the air.Advantages: Wind is free. No waste or greenhouse gases produced.Disadvantages: Unpredictable source of energy. Wind farms can be unsightly and cause noise pollution.Tidal

Source:The pulling effect of the moon on the earth causes the oceans and seas to rise and fall. The movement of the rise and fall of the oceans and seas can be used to drive turbines.Advantages: A free source of energy. No waste or greenhouse gases produced. Tides are predictable.Disadvantages: Tidal barrages can affect the natural habitat of wildlife and impact the environment. Can only supply energy when the tide is moving in or out.Hydro

Source:Water stored in a large volume in a reservoir behind a dam. The potential energy of the water can be transferred to kinetic energy in the turbines.Advantages: Once the dam is built the energy is free. No waste or greenhouse gases produced. Very reliable source of energy.Disadvantages: Dams are very expensive to build. Dams cause flooding which seriously impact the environment and local habitats.Waves

Source:Waves are produced by the action of the wind on the seas and oceans.Advantages: A free source of energy. No waste or greenhouse gases produced.Disadvantages: Dependant on the strength of the waves. Needs to be capable of withstanding rough weather. Sites are limited to only areas where the waves are consistently strong.Geothermal

Source:Heat from under the earth in volcanic regions is used to heat water to produce steam for running turbines for generating electricity. In some cases it is used to heat water for heating.Advantages: No fuel needed Does no contribute to greenhouse gasesDisadvantages: Limited sites available. Hazardous gases can be released from geothermal sites which require safe disposal.Biomass

Source:This is fuel obtained from decaying plant and animal material. Wood is one source as it can be burnt to provide heat energy. Sugar cane can be fermented to produce alcohol which can be used as a fuel.Advantages: Is a renewable source as long as plant and trees are replaced. Cheap and easily available source of fuel.Disadvantages: Produces greenhouse gases.Coal Fired Power StationBelow is an animation showing the main processes in generating electricity using coal as the fuel source. However, some further useful points are also worth mentioning.Flue Gas TreatmentCoal contains sulphur and when burnt it produces sulphur dioxide. Although, some sources of coal are low in their sulphur content some have a relatively high content. Low sulphur coals are usually more expensive.Sulphur dioxide is a greenhouse gas and also produces acid rain. In order to remove the sulphur dioxide from the flue gases produced, the power stations have flue gas desulphurisation plants. Removal of sulphur from the flue gas involves passing the gases through a scrubber. This is like a shower. The gases rise up the scrubber which showers water down on them. The sulphur dissolves in the water to give sulphurous/sulphuric acid, this way the sulphur is removed from the flue gas and the remaining gas passes up a chimney and into the atmosphere. The sulphurous/sulphuric acid produced flows out of the scrubber and is neutralised with limestone (calcium carbonate) to form calcium sulphate, water and carbon dioxide. The calcium sulphate produced is known as de-sulphanated gypsum and is sold to plasterboard/plaster manufacturers.Superheated SteamThis is steam at high pressure and above 100C.A Nuclear Power Station

The Uranium fuel rods are inserted into a large mass of moderator and are arrange in the reactor core to form the fuel assembly.

The moderator slows the neutrons down so they interact more strongly with the Uranium-235 nuclei. The fission reaction is regulated using cadmium control rods which absorb neutrons. The reactor core is housed in a reactor vessel constructed from steel 20 25 cm thick.

Coolant (either water or carbon dioxide at high pressures to prevent boiling) flow through the reactor core. Heat generated by the fission reaction is transferred to the coolant and removed from the core. The coolant then flows through a boiler where it transfers the heat from the reactor to water thereby generating steam.

The high pressure steam produced at the boiler is forced through the steam turbine. The steam turns the turbine blade which drives the turbine shaft. The generator is housed around the turbine shaft. A powerful electromagnet mounted on the turbine shaft produces electricity in the generator windings as it rotates.

The generated electricity goes to a transformer where the voltage is increased and transmitted along pylons.

The steam from the turbines is cooled in a condenser. Here it passes over a maze of pipes containing cold water sourced from a nearby water supply such as a river. The steam condenses to water and recycled back to the steam generator. The water in pipes sourced from the river is no much warmer after gaining heat from the steam and is cooled in a cooling tower.Wind TurbineWind is created from solar power, as the sun heats the air it rises above the cooler air creating an air current. A wind turbine consists of large propeller like blades which are rotated by the action of the wind. As the blades turn they spin and internal shaft connect to a generator thus transferring mechanical energy to electrical energy. As the primary source of energy is from the wind which is a clean renewable source of energy wind turbines do produce any pollution in the form of greenhouse gases. The animation below shows the workings of a wind turbine.The National GridThe national grid system is the network of cables which transport electricity from the power stations in Britain to homes, factories and other places that require it.Power stations produce electricity at high currents. Electricity transmission at high currents would encounter a large resistance in the transmission wire and therefore lose a lot of its energy as heat. To prevent this, the current generated is passed through a step up transformer. Here the voltage is increased to as much as 400,000V and the current decreased (remember the relationship P = VxI an increase in voltage and decrease in current by the same ratio will give the same power).The high voltage (400,000 Volts) electricity is carried along overhead lines and underground cables referred to as the supergrid. The voltage is the reduced in several stages making before reaching the end user. The voltage reduction is made in step down transformers.The diagram below gives a simplified representation of the National Grid system:

The Motor EffectBefore discussing the motor effect it is important to gain an understanding in magnets and magnetic field.Magnets are materials normally with iron in them that produce a magnetic field. They attract other pieces of iron bought close to them with a magnetic force.The region around a magnet where a magnetic effect can be felt is called the magnetic field.A magnet has two poles:1. North seeking pole or North Pole2. South seeking pole or south PoleThe magnetic field is strongest at its poles. The field around a magnet can be represented by lines with arrows on them. The arrows show the direction of the lines of force. Each field line starts at the North Pole and finishes at the South Pole.Magnets affect a wire conducting electricity; this is because an electric current in a wire produces a magnetic field. If a wire carrying a current is placed in a magnetic field of a magnet it will experience a force due to the interaction between the magnetic field of the magnetic and the magnetic field of the current in the wire.This force the electric wire experiences is called the motor effect and only happens when the wire is carrying electricity.The direction of the lines of force around a wire carry a current can be determined using the Right-hand Grip Rule. If you were to image gripping a wire carrying a current so that your right thumb pointed in the same direction as the flow of electrical current then the fingers of your right hand curl in the direction of the magnetic field lines.Right Hand Grip Rule

Flemings Left Hand RuleThe direction of movement of a current carrying wire in a magnetic field can be determined using Flemings Left Hand Rule.

By arranging your left hand as shown in the image above, the first finger points in the direction of the magnetic field (from North to South).The hand is then rotated until the second finger points in the direction of the current (remember conventional current is from positive to negative).The thumb then points in the direction of the movement of the wire.The summary below aids in memorising the rule.First Finger=Field(magnetic from North to South)

seCond Finger=Current(conventional current from +ive to ive)

thuMb=Movement of the wire

A Simple Electric MotorAn electrical motor is a device that converts electrical energy to mechanical energy. It works on the principle of the interactions between the magnetic fields of a permanent magnet and the field generated around a coil conducting electricity. The attractive and repulsive forces between the magnet and the coil create rotational motion.A simple electric motor consists of the following parts.1. A permanent magnet2. Armature or rotorThis consists of a thin copper wire coiled around an iron core, hence when electric current flows it acts as an electromagnet. In the case of a simple motor this is a wire loop.3. CommutatorA Commutator is a copper ring split in two halves. In a simple electric motor each half is connected to the ends of the wire loop. In practise they are connected to the axle.4. BrushesThe brushes connect the wire loop or armature to the power supply5. AxleIn electric motors the commutator is attached to the axle. The axle transfers the rotational motion.6. Power supply(battery)

Improving a MotorAn electric motor can be made powerful by the following; By increasing the number of turns that are wound on the coil. In the case of the wire loop in the animation this would mean winding to form two loops.

By winding the electrical wire around a soft iron core so that the magnetic field is stronger.

By replacing the permanent magnet with a electromagnet which can gice a stronger magnetic field.

By winding extras coils around the core. Similar to having two separate wire loops in the animation above however this would mean splitting the commutator into 4 parts.Principle of TransformersA transformer is a device that changes(transforms)and alternating potential difference (voltage) from one value to another value be it smaller or greater using the principle of electromagnetic induction.A transformer consists of a soft iron coil with two coils wound around it which are not connected to one another. These coils can be wound either on separate limbs of the iron core or be arranged on top of each other.The coil to which the alternating voltage is supplied is called the primary coil or primary winding. When an alternating potential difference is supplied the resulting alternating current in the primary coil produces a changing magnetic field around it. This changing field induces an alternating current in the secondary coil. The size of the induced voltage resulting from the induced current in the secondary coil depends on the number of turns in the secondary coil.The relationship between the voltage and the number of turns in each coil is given by:

Transformers can be of two types:Step-up TransformerOn a step-up transformer there are more turns on the secondary coil than the primary coil. The induced voltage across the secondary coil is greater than the applied voltage across the primary coil or in other words the voltage has been stepped-up.Step-down TransformerA step down transformer has less turns on the secondary coil that the primary coil. The induced voltage across the secondary coil is less the applied voltage across the primary coil or in other words the voltage is stepped-down.Transformers are very efficient. If it is assumed that a transformer is 100% efficient (and this is a safe assumption as transformers may be up to 99% efficient) then the power in the primary coil has to be equal to the power in the secondary coil, as per the law of conservation of energy.Power in primary coil = Power in secondary coilRemember, power = potential difference x currentThus,Primary coil p.d. x primary coil current=Secondary coil p.d. x secondary coil currentVPx IP=VSx ISSo if the potential difference is stepped up by a transformer then the current is stepped down by roughly the same ratio. In the case of the potential being stepped down by the transformer then the current is stepped up by the same ratio.