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**P1a Energy & Energy Resources**

Ks4 Core Science Mr D Powell

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3 Electrical Energy p254 K Learn examples of everyday electrical devices designed to bring about particular energy transformations. The power of an appliance is measured in watts (W) or kilowatts (kW). But energy is normally measured in joules (J). S to compare and contrast the particular advantages and disadvantages of using different electrical devices for a particular application. to calculate the amount of energy transferred from the mains using: E = Pt (kilowatt-hour, kWh) (kilowatt, kW) (hour, h) to calculate the cost of energy transferred from the mains using: total cost = number of kilowatt-hours x cost per kilowatt-hour U The amount of electrical energy a device transforms depends on how long the appliance is switched on and the rate at which it is transferred. Electricity is transferred from power station to consumers along the National Grid. The uses of step-up and step-down transformers; increasing voltage (potential difference) reduces current, and hence reduces energy losses in the cables.

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3.1 Electrical Devices p254 (K) Learn examples of everyday electrical devices designed to bring about particular energy transformations. (S) to compare and contrast the particular advantages and disadvantages of using different electrical devices for a particular application.

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S Electrical Devices In a pair list all the electrical devices you can see. Cooker Coffee pot Kettle Microwave Food Processor Radio Washing Machine Iron Hoover

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M Electrical Devices Consider the following things for each item you see; Mains or Battery powered? Useful Energy in Wasted Energy How is efficiency improved?

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**Can you identify forms of useful energy and wasted energy in different household devices?**

Battery or mains? Useful energy Energy wasted Efficiency Electric kettle M Thermal Thermal/ Sound Lid put on top Computer Electrical / Light CPU fans can run slower to save energy, monitor turns off Portable CD player B Kinetic / Sound Auto off switch, motor only runs when you press play Lamp Light Use special efficient bulbs Electric bell Current only flows when the button is pressed. Device Battery or mains? Useful energy Energy wasted Efficiency Electric kettle Computer Portable CD player Lamp Electric bell

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H Efficiency? Now you have thought about these devices in an “energy” way do the following; On a double page spread draw a bubble for each one with their names i..e “Laptop PC” Draw out spider lines and describe or annotate any ideas you have for how they can be modified /redesigned to become more efficient and reduce the energy they waste Estimate a Sankey Diagram...

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P Efficiency? Can you complete your own estimated Sankey energy diagrams for each device you studied today. You nee to list input energy, useful out energy, wasted energy & estimate the quantities in joules.

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3.2 Electrical Power p256 (K) The power of an appliance is measured in watts (W) or kilowatts (kW). But energy is normally measured in joules (J).

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**Which word links all of these images...**

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**Power of your leg muscles = ET / time for 50 steps**

Power Practical... 1) This practical involves stepping on and off a box or step. Use bathroom-type scales and measure your weight . Then measure the height of the box or “step” . The gain of gravitational potential energy of someone stepping onto the box (in joules) E = mgh (eq1) 2) Time how long it takes to make 50 steps onto and off the box. The gain of gravitational potential energy in making 50 steps on to the box; ET = 50 the gain in one step. ET = 50 mgh (from eq1) Power of your leg muscles = ET / time for 50 steps P = ET / t 3) Write down any calculations you have made and explain them 4) Why would the input power be more than the output power?

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**Power Practical... h = 0.16 m t= 57s W = 560N ET /t = Power**

Power = (50 mgh) / t = 50 x 560N x 0.16m / 57s = 80W

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**Formulae Extension... A/A***

We can also do something clever when thinking of this formula when looking at Kinetic Energy as well. EGPE = mgh (eq1) EKE = 0.5mv (eq2) If I think of a transfer involving the energy at the top of a waterfall (GPE) and energy at the bottom (mainly KE) I can work out the speed of the water falling by equating the two equations and assuming all the energy is transferred to kinetic. In every case we find a value of “g” gravity as 10 m/s2

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**What is the speed of the water...**

Using this idea can you apply the formula and fill in the grid for water which drops from different heights. You will need to use the Sqrt button on your calculator... h (m) V (in m/s) 5 10 14.14 20 100 44.7 h (m) V (in m/s) 5 10 20 100

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**Exam Question (C/D) 1000J EGPE = mgh or EGPE /gh = m**

A weight-lifter transfers 1000 J of energy to a weight when the weight is raised 1.6m in a time of 2.0 s. What is the change in Potential Energy? What is the mass lifted? Calculate the energy per second transferred to the weight by the weight-lifter? 1000J EGPE = mgh or EGPE /gh = m 1000J / (10 x 1.6m) = 62.5kg E = Pt so E/t = P J/2s = 500W

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**Exam Question II (B/C) 24,000J E=Pt so E = 800W x 120s = 96,000J**

In a hospital electronic arm an 800 W electric motor is used to raise a small load. In 120 s, the load gains J of gravitational potential energy from the motor. What is; The electrical energy supplied to the motor. Energy wasted by the motor. The efficiency of the motor. The output power of the motor 24,000J E=Pt so E = 800W x 120s = 96,000J so energy wasted is = 96,000-24,000 = 72,000J 24,000J / 96,000J = 0.25 or 25% 800W x 0.25 = 200W

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**Useful energy transferred (J) Useful energy transferred (J)**

Power & Efficiency... The table below shows the time taken by different electrical devices to transfer a given amount of energy supplied. The useful energy transferred in this time is also stated. Copy and Complete the table.... Device Time taken (s) Energy supplied (J) Useful energy transferred (J) useful power (W) Efficiency Lamp 1000 20 000 20 0.2 Microwave oven 120 96 000 48 000 400 0.5 Motor 300 18 000 6000 0.33 Computer 3000 33.3 0.11 Device Time taken (s) Energy supplied (J) Useful energy transferred (J) useful power (W) Efficiency Lamp 1000 20 000 Microwave oven 120 96 000 48 000 Motor 300 18 000 6000 Computer 3000

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**Units & Quantities Match Up**

Energy Power Temperature Mass Force watt Joule kilogram Newton degree Celsius C kg N J W

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**3.3 Using Electrical Energy p258**

(U) The amount of electrical energy a device transforms depends on how long the appliance is switched on and the rate at which it is transferred. (S) to calculate the amount of energy transferred from the mains using: E = Pt (kilowatt-hour, kWh) = (kilowatt, kW) x (hour, h) (S) to calculate the cost of energy transferred from the mains using: total cost = number of kilowatt-hours x cost per kilowatt-hour

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S What has happened here....

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**Power = Current x Voltage**

Joule Meter A joule meter counts the number of electrons moving around a circuit. It works them out as whole Joules of energy. We can work out the Power or energy transferred per second by a device by connecting a Joule meter up to a circuit. You teacher will demonstrate both types and show you how it works. Also you can see that there is a special formulae for Power; Power = Current x Voltage

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**Results experiment Theory**

Bulb Joules (J) Time (s) Power (W) Current (A) Voltage (V) 24W 300 12 25 2 24 36W 350 10.16 34 3 36 We have compared two types of bulbs using theory and actual counting of joules of energy flowed. Theory tells us that Power = Current x Voltage Experiment tells us that Power = Energy Flowed / time Obviously in our experiment there is a little bit of error and difference!

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**Understanding Electricity Bills**

Poor Dr Frankenstein did not look at his electricity bill and check the cost of each unit of electricity. Electricity is not only measured in Joules but as a larger chunk called a “Unit” Units are how we cost out domestic electricity. 1 Unit = 1KW hour of electricity. They are shown on the bill here..

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T kWh & Appliances.... The idea of this is quite simple. We know that appliances transfer energy in Joules. We can represent this transfer over a period of time by saying the number of joules which flow in a certain time period. This brings us onto the idea of “Power” in watts or 1W = 1J/s. Also we can say that 1kW = 1000J/s Well if we take this further and say that a kilowatt hour is simply; 1 kW x 1 hour. So now by using this idea we can compare devices by their value of kw hours

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Examples of kWh A 200 watt T.V set ……..transfers 1 kWh of energy if it is switched on for 5 hours A 500 watt vacuum cleaner……..transfers 1kWh of energy if it is switched on for 2 hours

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**Energy Efficiency Ratings**

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E kWh & Appliances.... Look at this example of three appliances. One old and two new The digital reading was taken to show their Power use over 24 hours. Old Fridge Freezer kWh old Fridge/Freezer (roughly 6ft high, half fridge, half freezer) consumed 3.93 kWh’s in 24hrs. Rating “E” New Fridge kWh new energy rating ‘A’ fridge (large fridge, 5ft high) consumes 0.34 kWh’s in 24hrs. New Freezer kWh new energy rating ‘A’ freezer (normal under-counter size) consumes 0.46 kWh in 24hrs.

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e kWh & Appliances.... Look at this example of three appliances. The digital reading was taken to show their Power Old Fridge/Freezer = 3.93 x p = 42p per day = £153 per year. (rated E) New Fridge = 0.34 x p = 3.6p per day = £13 per year. (A-rated) New Freezer = 0.46 x p = 4.9p per day = £18 per year. (A-rated) The saving would be £153 - £13 - £18 = £122 per year. That’s just the financial saving, add to this the environmental benefits

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Saving Energy You can save some energy by putting a device on standby. However, they still use a little bit of power. Here are some examples... DVD player on standby - 4 watts DVD player on but not playing - 10 watts DVD player playing a disk - 14 watts Laser Printer on standby - 3 watts Laser Printer Printing watts Dehumidifier on standby - 9 watts Dehumidifier working watts Desktop PC watts PC Peripherals - 36 watts PC & Peripherals watts Sky+ on Standby - 13 watts Sky+ Playing - 20 watts

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H Energy Costs... Look at this list of items and their cost in electricity. See if you can work out any costs of things that you can do or how you could save energy. Write a list in your book? 12hrs PC and Peripherals kWh = 18p per day = £68 per year 40 degrees wash kWh = 8p per wash = £8.50 per year 60 degrees wash kWh = 15p per wash = £15 per year 45 minutes walking on the treadmill kWh = 2.2p Boil 1.7 litres of cold water kWh = 2p Boil minimum level of cold water kWh = 0.4p Toast 2 slices of bread kWh = 0.4p 24hrs Sky+ on standby kWh = 3.3p per day = £12 per

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**P Cost of electricity. 38.4p 24p 16p 8p 0.8p**

If each unit of electricity costs 16p. Copy the information into a grid then work out what each device cost Power (kw) x time (hours) x cost per unit = monetary cost 38.4p 24p 16p 8p 0.8p 1000W = 1kW 100W = 0.1kW

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P Fill in the blanks

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3.4 The National Grid p260 (U) Electricity is transferred from power station to consumers along the National Grid. (K) The uses of step-up and step-down transformers; increasing voltage (potential difference) reduces current, and hence reduces energy losses in the cables.

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**What is the National Grid**

The “grid” is a system of cables which link Power Stations to homes, businesses, industry and other infrastructure. Along the way it has to modify the electrical current to make sure that as much of the energy is delivered as possible. Transformers do the modifications! This diagram shows the main routes.

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**Who produces the power. The power comes from a variety of sources.**

The map shows all the nuclear power stations The house here is putting energy back into the grid from its solar panels.

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Transformers These are really basic devices we can change the voltage and current at which the energy is transferred. The idea of this is to save power. (we will come to this shortly) The simple circuit consists of a Power supply, two bulbs and a transformer. The current to the lower bulb is transferred indirectly by a magnetic field induced in the iron loop. The current has been transformed and p.d. has increased and current reduced

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**Transformers & everyday uses...**

Here is an example of how we can transform voltages and currents. The core is the same as in the previous slide but now you can see that the number of turns of wire are different. The ratio of turns either steps up or steps down the voltage. What happens is when the current flow (alternating current) flows back and fourth in one set of wires it creates (induces) a current in the other set of wires. This example is a travel adapter plug!

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**Stepping up / Stepping Down**

132kV Power station Step up transformer Step down transformer Homes 25kV 230V If we keep the voltage the same all the way and wanted the process to be 90% efficient. Throughout the grid we would have to use cables that were 13cm in diameter! They would weight 7000 tonnes . They If we step up the voltage to 132kV the cables would be 4mm in diameter but we would still only lose 10% of the energy in heat. Also home electricity would be dangerous at such high voltages so it must stepped down anyway.

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Revision... Copy the diagram and complete the questions in your books on the National Grid Power station Step up transformer Step down transformer Homes We use the national grid to _ _ _ _ _ _ energy to our homes. The step-up transformers increase the _ _ _ _ _ _ _ _ and reduce the _ _ _ _ _ _. The high voltage electricity now at _ _ _ kV moves with _ _ _ thermal losses and means that the wires can be quite _ _ _ _. Finally the step-down transformers mean that the _ _ _ _ _ is reduced to _ _ _ V and is useable in every day appliances. This can only be done with _ _ _ _ _ _ _ _ _ _ _ from a power station. transfer voltage current 132 low thin voltage 230 alternating current.

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M An Argument.... Should power cables be underground or overhead? Here are some of the arguments used: They take up valuable land. They are more difficult to repair. They are more difficult to install across roads, railways and canals. They are much more expensive. They spoil the landscape. They produce electric and magnetic fields that might affect people. Which of the above arguments would you use to argue against: Underground power cables? Overhead power cables? TASK Imagine you are a spokesperson for an environmental group or power company going on live radio. Write down an argument using your own and these ideas from a perspective....

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**National Grid.... Complex version...**

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How much do we generate These figures are a big out of date but give the breakdown by source up to The amount is staggering!

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**Use as marked & for SEN or to save time on writing!**

Pages below this are extras and resources to quick print out that fit into the sequence of lessons. Use as marked & for SEN or to save time on writing!

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**to calculate the amount of energy transferred from the mains using: **

K Learn examples of everyday electrical devices designed to bring about particular energy transformations. The power of an appliance is measured in watts (W) or kilowatts (kW). But energy is normally measured in joules (J). S to compare and contrast the particular advantages and disadvantages of using different electrical devices for a particular application. to calculate the amount of energy transferred from the mains using: E = Pt (kilowatt-hour, kWh) (kilowatt, kW) (hour, h) to calculate the cost of energy transferred from the mains using: total cost = number of kilowatt-hours x cost per kilowatt-hour U The amount of electrical energy a device transforms depends on how long the appliance is switched on and the rate at which it is transferred. Electricity is transferred from power station to consumers along the National Grid. The uses of step-up and step-down transformers; increasing voltage (potential difference) reduces current, and hence reduces energy losses in the cables.

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**to calculate the amount of energy transferred from the mains using: **

K Learn examples of everyday electrical devices designed to bring about particular energy transformations. The power of an appliance is measured in watts (W) or kilowatts (kW). But energy is normally measured in joules (J). S to compare and contrast the particular advantages and disadvantages of using different electrical devices for a particular application. to calculate the amount of energy transferred from the mains using: E = Pt (kilowatt-hour, kWh) (kilowatt, kW) (hour, h) to calculate the cost of energy transferred from the mains using: total cost = number of kilowatt-hours x cost per kilowatt-hour U The amount of electrical energy a device transforms depends on how long the appliance is switched on and the rate at which it is transferred. Electricity is transferred from power station to consumers along the National Grid. The uses of step-up and step-down transformers; increasing voltage (potential difference) reduces current, and hence reduces energy losses in the cables.

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H An Argument.... Should power cables be underground or overhead? Here are some of the arguments used: They take up valuable land. They are more difficult to repair. They are more difficult to install across roads, railways and canals. They are much more expensive. They spoil the landscape. They produce electric and magnetic fields that might affect people. Which of the above arguments would you use to argue against: Underground power cables? Overhead power cables? TASK Imagine you are a spokesperson for an environmental group or power company going on live radio. Write down an argument using your own and these ideas from a perspective....

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H An Argument.... Should power cables be underground or overhead? Here are some of the arguments used: They take up valuable land. They are more difficult to repair. They are more difficult to install across roads, railways and canals. They are much more expensive. They spoil the landscape. They produce electric and magnetic fields that might affect people. Which of the above arguments would you use to argue against: Underground power cables? Overhead power cables? TASK Imagine you are a spokesperson for an environmental group or power company going on live radio. Write down an argument using your own and these ideas from a perspective....

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