P5 Electric Circuits Route map Over the next 12 lessons you will study : Friday 21 October 2011 P5.1 Static electricity P5.2 Electric Charge & Circuit symbols P5.3 Simple Circuits P5.4 Electric Current End of module test P5.5 Controlling Current P5.6 Measuring resistance P5.7 Resistors in circuits P5.8 Measuring Voltage P5.9 Electrical Power P5.10 Domestic Appliances P5.11 Generating Electricity P5.12 Distributing Electricity
Friday 21 October 2011 PLTS Independent enquirers Creative thinkers Reflective learners We will focus on Team workers Effective participators Self managers Literacy: Circuits, current, charge, electrons, resistors, series, parallel, resistance, connected, components and total resistance. Numeracy: The total resistance of 8 , 4 and 2 connected in series is 14 The total resistance of 8 , 4 and 2 connected in parallel is 7/8 First activity: In your book - draw a series circuit with 3 batteries (cells) facing the same direction, one switch on the negative side of the battery and then a light bulb, a resistor and a variable resistance. Now put a voltmeter and an ammeter into the circuit so that you can find the resistance of the light bulb. <ul><li>Lesson objectives: </li></ul><ul><li>Understand that when resistors are joined in series the overall resistance is bigger and that when resistors are joined in parallel the overall resistance is smaller </li></ul><ul><li>Understand that in complex circuits and printed circuit boards, resistors are used to control the flow of charge through a component or device </li></ul>P5.7 Resistors in circuits
P5.7 Resistors in circuits Friday 21 October 2011 Introduction: When resistors are joined in series the overall resistance is bigger because the battery now has to push the current through both resistors. When resistors are connected in parallel the overall resistance is smaller because the current/charge has at least 2 or more paths (branches) that it can take. So some current flows through one resistor and some flows through the other resistor. Resistors used in circuits to control the moving charge through a component can be made from metals with varying levels of conductivity. Variable resistors are made by changing the length of wire that the current flows through, that is: the longer the wire – the bigger the resistance (If you double the length you double the resistance.) Extension questions: 1: A hairdryer uses mains voltage (230 V). It takes a current of 5A. What is the resistance ? 2: A toy tractor has a 4.5 V battery operated motor. The resistance of the motor is 15 Ω. What is the current ? 3: A torch has resistance 120 Ω and the current is 0.1 A. What is the battery voltage ? 4: A series circuit has three bulbs, bulb A has a resistance of 2 bulb 2 has a resistance of 3 and bulb C has a resistance of 5 Work out the total resistance of the circuit Know this: a: Resistance in series R T = R 1 + R 2 + R 3 Resistance in parallel R T = 1/R 1 + 1/R 2 + 1/R 3 b: Resistance of a wire R = ρ l /A ρ is the resistivity, l the length and A the cross sectional area
Key concepts P5.7 a Look at the photograph and information and answer all the questions: Work out the total resistance of a circuit with three resistors ins series will the following values R1 0.5 R2 1.2 and R3 1.7 ? Looking at the series and parallel circuits explain why the total resistance for parallel circuit is always less than the value for the lowest onhmic resistor ? Resistors are used to control or reduce the amount of current flowing through complex circuits. Resistors in series : You can find the total resistance by adding up the value of each resistor. Total resistance in series = R 1 + R 2 + R 3 Resistors in parallel : The total resistance of the circuit is always less than the value of the smallest resistor. Total resistance in parallel = 1/R 1 + 1/R 2 + 1/R 3 Using resistors in complex circuits - + - + R 1 R 2 Resistors in series Resistors in parallel R 3 R 1 R 2 R 3
Key concepts P5.7 b Look at the photograph and information and answer all the questions: Look at circuit one, it has been solved for you, work out the total resistance in circuit 2, 3 and 4 ? Give three device where the current flow is controlled by resistors (variable of fixed) ? Resistance in circuits and electrical wires causes the heating effect. In most appliances, for example computers, this effect is an unwanted consequence of current flow. In all computers, a cooling fan is essential to prevent the fragile circuit boards and chips becoming overheated and damaged beyond repair. Resistance also wastes energy and therefore costs money. In some devices like a toaster, high resistance wire is used to produce the heating effect Using resistors in complex circuits to control voltage - + - + Circuit one Circuit two V V V V 12 V 12 V 4 V 8 V 2 V ? V 10 Ω 20 Ω 2 Ω 10 Ω - + - + Circuit three Circuit four V V V V 24 V 240 V 12 V ? V 60 V ? V 5 Ω 5 Ω 3 Ω 9 Ω
P5.7 Plenary Lesson summary: series parallel path resistance Friday 21 October 2011 A thermistor or temperature dependent resistance can be used to switch on an immersion heater when the temperature of the water in a tank falls below a particular value ( o C) and switch the heater off when the temperature of the water has risen to the required temperature. This allows you to have a ready supply of hot water when you need to shower or wash. How Science Works: Research about potential difference or voltage and fins out about the scientist Alessandro Volta. Preparing for the next lesson: The total ________ in Ohms is biggest when resistors are placed in _______ and smallest when they are placed in parallel. This is because when they are in ________ to one another, the current can flow down more than one __________. Decide whether the following statements are true or false : False True 3: If you change the material the wire is made from the resistivity will change ? False True 2: You can measure resistance with an ohmmeter ? False True 1: If the length of a wire is doubled the resistance will be halved ?
P5.8 Measuring Voltage Friday 21 October 2011 Literacy: Volts, voltmeter, potential difference, energy transfer, circuit, battery, components, push, jolt, terminals, battery, positive, and negative. Numeracy: If the voltage across one motor, one buzzer and a bulb in series is 1V, 1.5V and 0.5 V, then the total voltage coming from the battery is 3V (1V + 1.5V + 0.5 V) PLTS Independent enquirers Creative thinkers Reflective learners We will focus on Team workers Effective participators Self managers <ul><li>Lesson objectives: </li></ul><ul><li>Understand that voltage is measured in volts and that voltage (potential difference) across part of a circuit is be measured by placing a voltmeter in parallel with that part of the circuit. </li></ul><ul><li>Understand that in a series circuit the total voltage (V T ) across the batteries is equal to the sum of the voltages across each bit of the circuit (V 1 + V 2 + V 3 ) </li></ul>First activity: In your book or on your mini white board - draw a three branch parallel circuit with one battery with a voltage of 12 V. In the circuit, one light bulb is located on the first branch, two light bulbs on the second branch and a three light bulbs on the third branch. What would be the voltage across the bulbs found in a) the first branch b) the second branch and c) the third branch.
P5.8 Measuring Voltage Friday 21 October 2011 Introduction: The voltage of a battery can be thought of as the ‘push’ that the battery exerts on the charges in the circuit. It is also equal to the work done (energy) in moving a unit charge through a circuit. Another name for voltage is potential difference (pd). The bigger the voltage or p.d the bigger the push on the charge and the bigger the current flow. The effect of a bigger voltage on the current flow is very similar to that of a bigger height drop on the flow of water over a water fall. In a series circuit the voltage drop across the battery is equal to the total of all the voltage drops across each component in the circuit i.e V T = V 1 + V 2 + V 3 and is like a waterfall going down in steps. Know this: a: Energy = VQ where Energy is measured in joules (J), V is the voltage in volts (V) and Q is the charge in coulombs (C) b: Energy = VIt and Q = It where I is the current in amps (A) and t is the time in seconds (s) Extension questions: 1: If the current is 2A, how many coulombs of charge will flow in 10 s ? 2: The current is now increased to 3A, how many coulombs of charge will flow in one minute 3: How much energy is released by 5V pushing 4C of charge through a circuit ? 4: How much heat energy will be produced by a kettle powered by a voltage of 230V and a current of 10A, in one second?
P5.8 a Look at the photograph and information and answer all the questions: Voltage (V) or potential difference is measured in volts. The larger the voltage, the more energy or ‘push’ each electron is given. This energy is then transferred to the surroundings by a device like a bulb, motor, or buzzer. Voltage is measured using a voltmeter which is connected in parallel across a battery or device like a bulb or a buzzer. In a circuit, the cell or battery provides the voltage or potential difference needed to make a current flow . In the simple circuit shown opposite above left, explain what the voltage would be across the bulb ? If you added an extra bulb making three in total what would the voltage be across each bulb. Explain why, in series circuits, why as we add bulbs do they all become dimmer ? In the simple circuit shown opposite below left, the voltage of the battery remains the same at 6 volts. What would be the voltage across each the two bulbs ? Understanding voltage Key concepts + - 6V V + - 6V + - 6V V + - 6V V3 V2 V1
Key concepts P5.8 b Look at the photograph and information and answer all the questions: Explain how you would measure voltage across component like a bulb, motor or buzzer ? Explain why a watch only require a very low voltage of around 1.5 volts and a tube train require a very high voltage of around 11,000 volts ? Voltage of a battery as a measure of the ‘push’ it exerts on the moving charge around a closed circuit. Low voltage devices like mp3/4 players, watches and mobile phones require little energy and are usually powered by 1.5 or 3 volt batteries. High voltage devices like kettles, eclectic toasters, drills and cookers that requires lots of energy are supplied with domestic voltage at 230 volts. An electric chair uses electricity at 10,000 volts. Voltage use by different appliances A watch requires a voltage of 1.5 volts because it requires very little energy to move, the second, minute and hour hands. A kettle draws a current of 13 amps because it requires a medium amount of energy carrying electrons to boil water. A cooker requires a voltage of 230 volts because it requires lots of energy carrying electrons to heat food by using the oven.
P5.8 c Look at the photograph and information and answer all the questions: Explain using the model (opposite left) why as you add bulbs in a series circuit they become dimmer ? In both a series circuit with three bulbs and a parallel circuit with three braches and three bulbs (see circuit diagrams opposite left) we can use the water pump model to show what happens and how energy is transferred: Series circuit: The pump (battery) increases the potential energy of the water (electrons) The energy is then transferred in three steps as it moves through the bulbs. Parallel circuit: The water pump model also explain why the brightness of bulbs doesn’t change in a parallel circuit. The water (electrons) divides into three streams (branches). Each losing its energy in a single step when going through the bulb. Explain using the model (opposite left) why as you add bulbs in a parallel circuit they stay the same brightness ? Key concepts + - 6V + - 9V + - 6V + - 9V Voltage in series and parallel circuits parallel series
P5.8 Plenary Lesson summary: same parallel sum total Friday 21 October 2011 The rating plate on any electrical appliance like a kettle or a television tells you about the input voltage required and the power in watts that the appliance uses. An electric drill, for example will have an input voltage of 230 volts, a power rating of 690 watts. It will therefore draw a current of 3 amps (690W/230V). How Science Works: Research into the input voltage, the current drawn and the power rating for five different electrical appliances found in your home. Copy them into your book. Preparing for the next lesson: A voltmeter should always be placed in _______ with the voltage being measured. In a parallel circuit the voltage across each parallel section is the ________. In a series circuit the ________ voltage is equal to the ______ of individual voltages. Decide whether the following statements are true or false : False True 3: The bigger the voltage the bigger the current flow ? False True 2: If two batteries are connected in parallel the voltage will stay the same ? False True 1: The voltage across each branch of a parallel circuit is the same ?
P5.9 Electrical Power Friday 21 October 2011 PLTS Independent enquirers Creative thinkers Reflective learners We will focus on Team workers Effective participators Self managers First activity: Use the efficiency equation above to work out the energy efficiency of a) 20W compact fluorescent lamp producing 5W of light and b) a 690 watt toaster producing 600 watts of heat energy ? <ul><li>Lesson objectives: </li></ul><ul><li>Understand know that power is measured in watts (W) and is equal to the energy transferred per second or the rate of doing work </li></ul><ul><li>Understand that the efficiency of a device = the energy converted to useful work </li></ul>Literacy: Power, Watts, voltage, current, time, work done, energy transferred efficiency, input energy, output energy and percentage. Numeracy: The efficiency of an incandescent filament light bulb is only about 13%. That means that 94% of the energy used is converted into heat energy instead of light. The energy efficiency of a energy saving light bulb is about 80%. the energy supplied by the electricity supply
P5.9 Electrical Power Friday 21 October 2011 Introduction: When an electric current flows in a circuit, energy is transferred from the power supply to the components in the circuit. The rate of transfer of energy is called power and is measured in watts (W) Power = Energy/time and Power = Voltage x Current ( P = V I ) If the battery voltage is doubled the power is quadrupled. This is because when the battery voltage doubles so does the current. Energy transfer in electrical appliances is always less than 100% efficient. This is because some of the energy supplied to the appliance is wasted as other forms of energy such as heat energy or sound energy Extension questions: 1: The power supplied to a light bulb is 60W, but only 3W is radiated as light energy. How much power is wasted? 2: Using the equation efficiency = useful power out/power in work out the efficiency of the light bulb above? 3: What happens to the energy that does not leave the light bulb as light ? 4: Another student says that you could use the equation efficiency = useful energy out/energy in. Is she right? Know this: a: P = VI where P is the power in watts (W) V is the voltage in volts (V) I is the current in amps (A) b: P = energy/time where energy is measured in joules time is measured in seconds
Key concepts P5.9 a Look at the photograph and information and answer all the questions: A 12 V cell passes a current of 10 A through a car starter motor for 10 seconds. How much energy is transferred from the battery to the lamp ? Using E = V x I x t (12 V x 10 A x 10 s) ? A 3 V cell passes a current of 2 A through a bulb for 1 minute. How much energy is transferred from the battery to the lamp ? Using E = V x I x t (3 V x 2 A x 60 s) ? Think of a simple series circuit that you might find in a torch which includes a cell, bulb and switch. As electrons flow around a circuit, they gain electrical energy in the cell and then lose this energy in the bulb as light and heat. The total amount of energy transferred or total charge to a device depends on voltage, current and time. Energy transfer in circuits + - + - + - + - + - + - + - + - + - + - power = 1 unit power = 2 units Double voltage or keep current the same power = 3 units Triple voltage or keep current the same power = 2 units Double the current or keep voltage same power = 3 units Triple the current or keep voltage same
P5.9 b Look at the photograph and information and answer all the questions: The power rating for any device tells us how much energy in joules over time is used. A cooker supplied with 230 volts and 30 amps has a power rating of 6900 watts (230 V x 30 A = 6900 W), therefore it uses 6900 joules every second. A light bulb is far less power hungry and is supplied with 230 volts and 0.4 amps, has a power rating of 92 watts (rounded up to 100 watts), therefore it uses 92 joules every second. Thinking about what each device does, explain why a kettle uses more energy (jS -1 ) than a filament light bulb ? In a simple circuit, what carries energy around the circuit from the power supply to a device like a bulb or buzzer ? Calculate how many joules is supplied to the following devices a) toaster (900W on for 30 S) b) Light bulb (100 Won for 10 S) and c) kettle (2000 W on for 120 S) ? Power (watts) = voltage (volts) x current (amps) Working out power Devices and their power ratings Key concepts 2.5 2.0 1.5 1.0 0.5 0.0 Toaster (900 W) Hair dryer (1500 W) Kettle (2000 W) 2,500 2,000 1,500 1,000 500 0 Watts Joules per second Light bulb (100 W)
P5.9 c Look at the photograph and information and answer all the questions: An energy efficient home uses less energy than a normal home. Saving energy is not just about reducing the amount of heat energy that escapes through the walls, floors, windows and loft space. We can also use energy efficient devices and a bit of common sense, for example turning off lights, boiling less water and wearing warm cloths indoors also saves energy. Look at the thermal image opposite left of a house during the winter months. Which parts of the house allow most heat to escape to the colder surroundings ? The home owners are advised to fit energy efficient double glazing...do you think this is sound advice ? Give three other ways that we can save energy and money on our energy bills at home, work or school ? Energy efficient ratings All devices from light bulbs to laptops now have to have an ‘energy efficiency rating’ by law. This tells us whether a product is energy efficient or inefficient. A rating is the best. G rating is the worst. Key concepts
P5.9 Plenary Lesson summary: Power watts energy equal Friday 21 October 2011 A fuse breaks the circuit if a fault in an appliance causes too much current to flow. This protects the wiring and the appliance if something goes wrong. The fuse contains a piece of wire that melts easily. If the current going through the fuse is too great, the wire heats up until it melts and breaks the circuit. How Science Works: Work out how many units of electricity were actually used or were estimated to have been used in your last home electricity bill. Preparing for the next lesson: Electrical _________ is the rate of doing work and is _______ to the energy transferred per second. Power is measured in _______. All electrical appliances are less than 100% efficient. Transformers are amongst the most _________ efficient appliances. Decide whether the following statements are true or false : False True 3: An appliance with a G energy rating is more efficient than one with an A rating ? False True 2: Power = Voltage x Current ? False True 1: An energy efficient light bulb is one that wastes the least amount of energy ?
P5.10 Domestic Appliances Friday 21 October 2011 PLTS Independent enquirers Creative thinkers Reflective learners We will focus on Team workers Effective participators Self managers <ul><li>Lesson objectives: </li></ul><ul><li>Understand that the energy use in a house is measured in kilowatt-hours </li></ul><ul><li>Understand that a one kilowatt fire left on for one hour will use up one kilowatt-hour of energy and that one unit on an electricity bill means one kilowatt-hour of electrical energy </li></ul>Literacy: Unit of electricity, kilowatt-hours, joules. Numeracy: There are 3.6 million joules of energy in one kilowatt – hour (how do we know this well, a device that consumes 1000 watts or 1 kilowatt will use 1000 joules every second. Over a hour that 1000 x 60 x 60 = 3,600,000 joules) First activity: Work out the total energy usage in joules or kilojoules of the following a) a 100 watt light bulb (230 volts 0.43 amps) left on for 10 seconds b) a 690 watt kettle (230 volts 3 amps) used for 2 minutes and c) a 1,000,000 watt electric chair (10,000 volts 100 amps) used for 2 minutes ?
P5.10 Domestic Appliances Friday 21 October 2011 Introduction: The amount of electrical energy transferred to an appliance depends on its power and the length of time it is switched on. The amount of mains electrical energy transferred is measured in kilowatt-hours, kWh. One unit of electricity is 1kWh. Electricity meters measure the number of units of electricity used in a home or other building. Units (kilowatt-hours) are used instead of joules because a joule is a very small unit of energy. The more units used, the greater the cost. Total cost = number of units x cost per unit The less energy that is wasted and the more efficient an appliance is, the fewer units are used. Extension questions: 1: How much does it cost to run a lamp for 1000 hours a) with a 60W bulb and b) an 11W bulb ? If electricity cost 8 pence for an 8 kWh ? 2: Work out how much money do you save by using the 11W bulb? 3: An electric fire is rated at 3kW. How much does it cost to use it for 800 hours. An electric oven is rate at 5 kW how much does it cost to cook a chicken which takes 2 hours to roast ? 4: It takes a 2 minutes to kill someone uses a 1000 kW electric chair. How much does it cost the state in electricity ? Know this: a: Know that Energy = power x time So: Number of kilowatt-hours = number of kilowatts x number of hours. b: Know that the total cost = number of units x cost per unit.
Key concepts P5.10 a Look at the photograph and information and answer all the questions: A device like a laptop or a television transforms electrical energy into other forms of energy. Some of the energy transformed is not useful and dissipates usually as heat to the surroundings. A filament light bulb converts electrical energy into heat and light energy, with only the light energy being useful. 150 joules of electrical energy 130 joules of heat energy 20 joules of light energy Input energy Output energy Energy efficiency of a filament electric light bulb compared to a energy efficient light bulb 150 joules of electrical energy 30 joules of heat energy 120 joules of light energy Input energy Output energy Sankey diagram Sankey diagram Energy efficient light bulbs create very little heat, therefore they waste very little energy. Explain why the government is right to ban the sale of filament light bulbs from 2011 ? Using a diagram show the energy transfers when using a) a hair dryer b) a toaster c) a television d) an electric fire and e) a laptop ? 150 J 130 J heat 20 J light electrical 150 J 30 J heat 120 J light electrical
Key concepts P5.10 a Look at the photograph and information and answer all the questions: Work out the three calculations for the Dyson, cooker and washing machine based on the power rating and time used ? Which would cost you more running a washing machine for 1 hour or cooking a chicken for 2 hours in a cooker ? The cost of using electrical appliance at home like a light bulb, cooker, computer and television is calculated using the Kilowatt hour. The electricity meter records how many kWh units of energy your house uses per year. Calculating the Kilowatt hour: Energy transferred (kWh) = Power (kW) x time (h) x cost of 1 kWh (£)… cost of 1 kWh = 8 pence The cost of electricity using kilowatt-hours A 500 W Dyson used for 30 minutes will cost 0.5 kW x 0.5 h x 8 pence = ………… ? 500W Dyson 5 kW Cooker 3 kW washer A 5 kW cooker/oven used for 2 hours will cost 5 kW x 2 h x 8 pence = ………… ? A 3 kW washing machine used for 45 minutes will cost 3 kW x 0.45 h x 8 pence = ………… ?
P5.10 c Look at the photograph and information and answer all the questions: We all have to pay for the electricity that we consume in our homes. In every home, you will find an electricity meter. This records the amount of electrical energy your home uses. The electricity company records the number of units (kilowatt hours) that you use every quarter by comparing the previous reading with the current reading Look at the bill opposite left, how many kilo-watt hours did the consumer use of the billing period ? Look at the bill opposite left a) what was the length of the billing period and b) what was the cost of electricity over that period and c) per day ? Give three ways in which you can save money at home by reducing your consumption of electricity ? A typical bill is sent every three months 1: Account number 2: Bill date 3: Customer address 4: Number of units used per day over charging period 5. Total amount due including all charges 1 2 3 4 5 Key concepts
P5.10 Plenary Lesson summary: hour electricity unit energy Friday 21 October 2011 You could get an electric shock if the live wire inside a cooker, comes loose and touches the metal casing. However, the earth terminal is connected to the metal casing so that the current goes through the earth wire instead of causing an electric shock. How Science Works: Research into how electricity is generated and distribute form the power station to the consumer ? Preparing for the next lesson: The amount of energy used by a one kilowatt appliance in an ________ is one kilowatt - hour. This would be marked on an electricity bill as one ______ of electricity. The amount of ________ used is measured in kilowatt-hours instead of joules because one joule of _______ is so small. Decide whether the following statements are true or false : False True 3: A 3 amp fuse should be used in a 600W 230V hairdryer ? False True 2: A 300W TV left on for 5 hours will use 1.5 kWh of energy ? False True 1: There are 1000W in a kW ?
P5.11 Generating Electricity Decide whether the following statements are true or false: <ul><li>Lesson objectives: </li></ul><ul><li>Understand that if a magnet is moved into and out of a wound copper coil, voltage and current are induced and that if the magnet is stationary, the current stops flowing </li></ul><ul><li>Understand that the current flow changes direction when the magnet changes direction </li></ul>Friday 21 October 2011 First activity: The last village to be supplied with electricity was the inhabitants of Cym Brefi in mid-Wales in May 2003. Explain why electricity is a) versatile b) easy to transport c) relatively safe to use and d) pollution free at the point of use ? What did the inhabitants use before this date to power their washing machines and vacuum cleaners ? Literacy: Electricity, electromagnetism, copper coil, dynamo, induced voltage, induced current, ferrous core, rotor, stator coils, rotor coil and a.c. output. Numeracy: Putting a soft iron core inside the coil can make the induced magnetic field as much as a 1000 times stronger, where compared to the current and voltage magnitude in the absence of a ferrous core. PLTS Independent enquirers Creative thinkers Reflective learners We will focus on Team workers Effective participators Self managers
P5.11 Generating Electricity Friday 21 October 2011 Introduction: Faraday discovered that when a magnet is plunged into a coil a voltage is induced in the coil so that current flows. If the magnet is moved out of the coil current flows again – but in the opposite direction! If the magnet is still (not moving) – no current flows! A bigger voltage and current is induced if: The magnet is moved faster; a stronger magnet is used, there are more turns on the coil or if the coil has a soft iron core Extension questions: 1: You have wound as many turns as you can on a soft iron core. What can you now do to produce a higher voltage (give two ways)? 2: Which of these appliances can work well from a battery because they do not need much current: a) toaster, b) torch, c) calculator or d) hair-dyer 3: Which of these appliances must have an d.c supply: a) washing machine, b) microwave, c) mobile phone or d) liquidiser ? 4: Most electricity in the UK is generated by fossil fuel powered power stations: Show the transfer of energy form fossil fuel to current inside a mains wire using a flow diagram ? Know this: a: Know that an appliance that produces heat such as a kettle can be worked by both a.c or d.c, as it does not matter which way current flows, heat energy is still produced b: Know that other appliances such as TVs and mobile phones have to convert a.c into d.c inside themselves to work.
Look at the photograph and information and answer all the questions: In 1831, Michael Faraday’s discovered that a moving magnetic field produced an electric current or flow of electrons inside a conducting wire. Faraday had demonstrated that when a wire crosses a magnetic field, a current is induced. Electromagnetic induction was a landmark in science, for it made possible cheap, clean, transportable and relatively safe electrical energy. Explain how Faraday’s discovery of electricity would have transformed the World back in 1831 ? A French scientist called Volta invented the first simple battery...what unit did he lend his name to ? Imagine a World without electricity...what three electrical devices would you find hardest to live without ? Inducing a current P5.11 a Key concepts Motion Current flow Magnet South North
Key concepts Look at the photograph and information and answer all the questions: The trace shows mains alternating current (a.c.) which changes direction 50 times a second (50 Hz.) What is a direct current (d.c.) ? In power stations huge turbines turning at 50 cycles per second produce mains electricity. What drives these turbine generators ? Dynamos and turbine generators found in power stations both generate electricity. They both have a coil of wire which spins at high speeds around a magnet. When the wire coil crosses the magnetic field, a voltage is induce inside the wire. There are three ways to increase the size of voltage induced in the copper coil: Use a stronger magnet, use a copper coil with more turns and spin the coli faster Generating alternating current (dynamo) P5.11 b Driver Axel Copper coil Iron core Magnet Contact Output Voltage +230V - 230V Time 0.1 Time 0.1 0.2 0.2 Voltage +230V - 230V Time 0.1 Time 0.1 0.2 0.2
Look at the photograph and information and answer all the questions: A large power station produces enough electricity for an entire city, supplying it with millions of watts of electrical power. A fossil fuel burning power station uses the chemical energy in fuels like coal, oil and gas and heats water producing steam which then drives a turbine generator. This induces an electrical current which is then transported to our homes. Name three devices at home that use electrical energy ? Fossil fuels were formed millions of years ago...explain why a) these are finite resources and b) why the energy trapped in these fuels originally came from the sun ? A scientist once said that fossil fuels were just to precious to just simply burn in order to produce heat energy...explain why this is true ? Chemical Heat Kinetic Electrical Energy transformation from fossil fuel to electricity Inside a fossil fuel power station P5.11 c Key concepts
Look at the photograph and information and answer all the questions: The world will need greatly increased energy supply in the next 20 years, especially cleanly-generated electricity. Electricity demand is increasing much more rapidly than overall energy use and is likely to almost double from 2004 to 2030. Nuclear power provides about 15% of the world's electricity, almost 24% of electricity in OECD countries, and 34% in the EU. Its use is increasing. Look at the map opposite left, it show in red and dark red the biggest users of energy. Which countries are the biggest users of energy ? Explain why the USA are the biggest users of energy ? Look at the graph opposite left a) explain how energy demand changes over a 24 hr period and b) when and why does peak demand happen ? P5.11 d Key concepts
P5.11 Plenary Lesson summary: voltage no changed magnet Friday 21 October 2011 A bicycle dynamo has a wheel that touches the back tyre. As the bicycle moves, the wheel turns a magnet inside a coil. This induces enough electricity to run the bicycle's lights How Science Works: Research into how electricity is distributed across the National grid and how transformers (step up and step down) work to change output voltage. Preparing for the next lesson: When a _______ is moved within a coil or a coil is moved around a magnet a _________ is induced which makes a current flow if the circuit is complete. If the pole of the magnet is changed or the movement direction ______ then the voltage and current flow also change direction. If there is ___ relative movement then there is no voltage or current induced Decide whether the following statements are true or false : False True 3: Using an RCCB on a lawnmower or power tool can save life ? False True 2: A TV converts ac into dc so that it can work ? False True 1: The faster a magnet is moved into the coil the greater the induced voltage ?
P5.12 Distributing Electricity Friday 21 October 2011 PLTS Independent enquirers Creative thinkers Reflective learners We will focus on Team workers Effective participators Self managers <ul><li>Lesson objectives: </li></ul><ul><li>Understand how transformers work to step up and down input and output voltage and current </li></ul><ul><li>Understand that 1: if the secondary coil of a transformer has more turns than the primary coil – it is a step up transformer and the output voltage is bigger and 2: if the secondary coil of a transformer has less turns than the primary coil – it is a step down transformer and the output voltage is smaller </li></ul>Literacy: Power station, electricity, turbine, generator, National grid, pylons, cables, transformers, primary coil, secondary coil, step–up, step-down and grid network Numeracy: Electricity is generated at around 25,000 volts. It is transported at 400,000 volts across a super grid network of pylons and cables. Mains electric is a mere 230 volts. This can be transformed down further to 12 or even 5 volts a.c. First activity: Think of four different way in which electricity is generated for example a coal fire power station. State which methods use fossil fuels and which use renewable technology ?
P5.12 Distributing Electricity Extension questions: 1: Which of these ( A to G ) are step-up transformers and which are step-down transformers ? A B C D E F G Number of primary coil turns 600 600 600 600 120 120 120 Number of secondary coil turns 30 300 1200 2400 60 240 960 2: If you had a 3 volts a.c. supply but your device needed a 6 volt a.c. supply how would you make a simple transformer to do this ? 3: When electricity is stepped up from 25,000 V to 400,000 V what gets smaller ? Know this: Vp/Vs = Np/Ns Vp is the voltage across the primary coil , Vs is the voltage across the secondary coil, Np is the number of turns in the primary coil, Ns is the number of turns in the secondary coil. Friday 21 October 2011 Introduction: Power stations produce electricity at 25,000volts, prior to its transport across a national grid to the consumer (homes, schools industry and transport) Step-up transformers are used at power stations to produce the very high voltages (275,000 or 400,000 volts) needed to transmit electricity through the National Grid power lines. At these high voltages, the current flow through the cables is much lower, so we waste less energy. Before electricity enters the home, high voltages step-down transformers are used locally to reduce the voltage to safe levels. The voltage of household electricity is about 230V, in industry between 11,000 and 33,000 volts.
Look at the photograph and information and answer all the questions: Electricity produced by power stations is transported to users by a network of cables, pylons, substations and transformers called the national grid. The majority of power stations in Great Britain use fossil fuels. There are other types of power stations that use alternative energy sources like nuclear power. There are also smaller generating stations that use renewable energy sources. Explain why most UK power station are found away from large cities like London ? Pylons are used to transport electricity around the countryside, however under-ground cables are used in urban areas...explain why ? Explain the journey from power station to a device like a light bulb found inside your home ? The national grid Power station Pylons and cables transformer Industry and households P5.12 a Key concepts
Look at the photograph and information and answer all the questions: The most common way to generate electricity is by heating water creating high pressure steam which then drives a turbine generator. Many different fuels can be burned to heat water including wood, coal, oil and natural gas. In a nuclear generating plant, a process called nuclear fission creates the heat by splitting uranium atoms. Name three devices that use electrical energy ? Explain why in recent years, use of traditional fuels has been supplemented with emerging technologies that use the sun, wind and even biomass ? We burn fossil fuels like coal and gas to produce heat energy, what was the original source of the energy trapped in these fossil fuels ? P5.12 b Key concepts
Key concepts Look at the photograph and information and answer all the questions: At power stations, are transformers use to lower or raise the voltage before transports across the nation grid ? Before reaching your home, how many transformers would have stepped up and stepped down the voltage form the power station ? Transformers can be used to step up or step down voltage. Most transformers at home are used to provide a low voltage power supply from high voltage domestic mains electricity for devices like computers, radios and televisions. These devices require low voltages because of their delicate components and circuit boards. A transformer uses alternating current in one coil to induce alternating current in another coil with a different and lower voltage. Transforming electricity Step up transformer: If the secondary coil has more turns than the primary coil then it is a step up transformer, because the secondary voltage is larger Step down transformer: If the secondary coil has fewer turns than the primary coil then it is a step down transformer, because the secondary voltage is smaller P5.12 c
Key concepts Look at the photograph and information and answer all the questions: A transformer contains two coils of wire, wound on an iron core. These wires are linked by the iron core. We can work out the output or input voltage or even the number of turns for the primary or secondary coil by using the following formula: Secondary voltage No. of turns on 2 nd coil V 2 = N 2 Primary voltage No. of turns on 1 st coil V 1 = N 1 P5.12 d Look at the three transformers above. You are given the input voltage and the number of turns on the primary and secondary coil. Work out; a) the output voltage b) whether it is a step up or step down transformer ? Primary turns (N 1 ) 100 turns 100 turns ? Secondary turns (N 2 ) 400 turns 50 turns 50 Input voltage (V 1 ) 10 V 20 V 10 V Output voltage (V 2 ) ? ? 5 V Step down/Step down ? ? ?
Look at the photograph and information and answer all the questions: Wind is moving air that has kinetic energy. This energy can be captured to drive a wind turbine generator. The blades are turned by the wind, which in turn makes a generator turn. This induces an electric current. Wind generators or farms are found in windy places like offshore. Although these wind farms don’t create pollution, many people object to how they spoil their view. Explain how a wind turbine can generate electrical energy ? Give three advantages and three drawbacks to using wind turbines rather than fossil fuel powered power stations? Why are the majority of wind farms here in the UK place offshore rather than on land ? P5.12 e Key concepts
P5.12 Plenary Lesson summary: small National 25,000V 400,000V Friday 21 October 2011 A transformer plugged into the mains, but not being used will still get warm as it is continuously transforming voltage from one value into another and heat energy is produced in the process. To prevent this waste of energy, transformers need to be unplugged when not in use. How Science Works: Revise the work done in this topic for your end of module test Preparing for the next lesson: In the ‘super’ Grid network of the _______ grid, transformers are used to step up the voltage produced in the power stations from ________ to ________ This is done so that the current in the pylon lines is _______ and so that there is less energy wasted in heating the pylon cables themselves. Decide whether the following statements are true or false : False True 3: It is the changing magnetic fields that induces the voltage ? False True 2: A step-down transformer is used to transform voltage from 230V to 6V ? False True 1: As power =VI, when the voltage is high the current is low ?