P1a Energy & Energy Resources Mr D Powell. Mr Powell 2008 Index Electrical Energy p254 3 3.

P1a Energy & Energy Resources

KS4 CORE SCIENCEMr D Powell

Mr Powell 2008Index

Electrical Energy p2543

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.

Mr Powell 2008Index

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.

Mr Powell 2008Index

Electrical Devices S In a pair list all the

electrical devices you can see.

Cooker Coffee pot Kettle Microwave Food Processor Radio Washing

Machine Iron Hoover

Mr Powell 2008Index

Consider the following things for each item you see;

1. Mains or Battery powered?

2. Useful Energy in

3. Wasted Energy

4. How is efficiency improved?

Electrical Devices M

Mr Powell 2008Index

Device Battery or mains?

Useful energy

Energy wasted Efficiency

Electric kettle

Computer

Portable CD player

Lamp

Electric bell

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

Device Battery or mains?

Useful energy

Energy wasted Efficiency

Electric kettle M Thermal

Thermal/Sound

Lid put on top

Computer M Electrical / Light Thermal

CPU fans can run slower to save energy, monitor turns

off

Portable CD player B Kinetic /

Sound Thermal Auto off switch, motor only runs when you press play

Lamp M Light Thermal Use special efficient bulbs

Electric bell B Kinetic / Sound Thermal Current only flows when the

button is pressed.

Mr Powell 2008Index

Now you have thought about these devices in an “energy” way do the following;

1. On a double page spread draw a bubble for each one with their names i..e “Laptop PC”

2. 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

3. Estimate a Sankey Diagram...

Efficiency? H

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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.

Efficiency? P

Mr Powell 2008Index

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).

Mr Powell 2008Index

Which word links all of these images... S

Mr Powell 2008Index

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?

Mr Powell 2008Index

Power Practical...h = 0.16 mt= 57sW = 560N

ET /t = Power

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

Mr Powell 2008Index

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 = 0.5mv2 (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

vh

vhg

vhg

mvhmg

mvhmg

20

2

2

2

2

1

2

2

2

Mr Powell 2008Index

What is the speed of the water...

vh

vhg

vhg

mvhmg

mvhmg

20

2

2

2

2

1

2

2

2

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

20

100

h (m) V (in m/s)

5 10

10 14.14

20 20

100 44.7

Mr Powell 2008Index

Exam Question (C/D) 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.

1) What is the change in Potential Energy?

2) What is the mass lifted?

3) Calculate the energy per second transferred to the weight by the weight-lifter?

1. 1000J

2. EGPE = mgh or EGPE /gh = m

1000J / (10 x 1.6m) = 62.5kg

3. E = Pt so E/t = P 1000J/2s = 500W

Mr Powell 2008Index

Exam Question II (B/C)In a hospital electronic arm an 800 W electric motor is used to raise a small load. In 120 s, the load gains 24 000 J of gravitational potential energy from the motor. What is;

1. The electrical energy supplied to the motor.2. Energy wasted by the motor.3. The efficiency of the motor.4. The output power of the motor

1. 24,000J

2. E=Pt so E = 800W x 120s = 96,000J so energy wasted is = 96,000-24,000 = 72,000J

3. 24,000J / 96,000J = 0.25 or 25%

4. 800W x 0.25 = 200W

Mr Powell 2008Index

Power & Efficiency...

DeviceTime

taken (s)

Energy supplied

(J)

Useful energy transferred

(J)useful

power (W) Efficiency

Lamp 1000 100 000 20 000

Microwave oven 120 96 000 48 000

Motor 300 18 000 6000

Computer 3000 900 000 100 000

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....

DeviceTime

taken (s)

Energy supplied

(J)

Useful energy transferred

(J)useful

power (W) Efficiency

Lamp 1000 100 000 20 000 20 0.2

Microwave oven 120 96 000 48 000 400 0.5

Motor 300 18 000 6000 20 0.33

Computer 3000 900 000 100 000 33.3 0.11

Mr Powell 2008Index

Units & Quantities Match Up PEnergy Power ForceTemperature Mass

watt Joule degree Celsiuskilogram Newton

C kg WN J

Mr Powell 2008Index

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

Mr Powell 2008Index

What has happened here.... S

Mr Powell 2008Index

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

Mr Powell 2008Index

ResultsBulb Joules (J) Time (s) Power (W) Current (A) Voltage (V) Power (W)

24W 300 12 25 2 12 24

36W 350 10.16 34 3 12 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!

THEORYEXPERIMENT

Mr Powell 2008Index

Understanding Electricity Bills T 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..

Mr Powell 2008Index

kWh & Appliances.... T 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

Mr Powell 2008Index

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

Mr Powell 2008Index

Energy Efficiency Ratings

Mr Powell 2008Index

kWh & Appliances.... E 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.

1. Old Fridge Freezer - 3.93 kWhold Fridge/Freezer (roughly 6ft high, half fridge, half freezer) consumed 3.93 kWh’s in 24hrs. Rating “E”

2. New Fridge - 0.34 kWhnew energy rating ‘A’ fridge (large fridge, 5ft high) consumes 0.34 kWh’s in 24hrs.

3. New Freezer - 0.46 kWhnew energy rating ‘A’ freezer (normal under-counter size) consumes 0.46 kWh in 24hrs.

Mr Powell 2008Index

Look at this example of three appliances. The digital reading was taken to show their Power

1. Old Fridge/Freezer = 3.93 x 10.668p = 42p per day = £153 per year. (rated E)

2. New Fridge = 0.34 x 10.668p = 3.6p per day = £13 per year. (A-rated)

3. New Freezer = 0.46 x 10.668p = 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

kWh & Appliances.... E

Mr Powell 2008Index

Saving EnergyYou 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 - 1000 watts

Dehumidifier on standby - 9 watts Dehumidifier working - 170 watts

Desktop PC - 112 watts PC Peripherals - 36 watts PC & Peripherals - 148 watts

Sky+ on Standby - 13 watts Sky+ Playing - 20 watts

Mr Powell 2008Index

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 - 1.76kWh = 18p per day = £68 per year

40 degrees wash - 0.77kWh = 8p per wash = £8.50 per year 60 degrees wash - 1.39kWh = 15p per wash = £15 per year

45 minutes walking on the treadmill - 0.21kWh = 2.2p

Boil 1.7 litres of cold water - 0.19kWh = 2p Boil minimum level of cold water - 0.04kWh = 0.4p

Toast 2 slices of bread - 0.04kWh = 0.4p

24hrs Sky+ on standby - 0.31kWh = 3.3p per day = £12 per

H

Mr Powell 2008Index

Cost of electricity. PIf each unit of electricity costs 16p. Copy the information into a grid then work

out what each device cost

38.4p 24p 0.8p16p 8p

Power (kw) x time (hours) x cost per unit = monetary cost

1000W = 1kW100W = 0.1kW

Mr Powell 2008Index

Fill in the blanks P

Mr Powell 2008Index

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.

Mr Powell 2008Index

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.

Mr Powell 2008Index

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.

Mr Powell 2008Index

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 reducedhttp://www.practicalphysics.org/go/Experiment_349.html

Mr Powell 2008Index

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!

Mr Powell 2008Index

Stepping up / Stepping Down

Power stationStep up

transformerStep down

transformer Homes

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.

25kV132kV

230V

Mr Powell 2008Index

Revision...

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.

Power stationStep up

transformerStep down

transformer Homes

Copy the diagram and complete the questions in your books on the National Grid

transfervoltage current

132 lowthin

230 voltagealternating current.

Mr Powell 2008Index

An Argument....Should power cables be underground or overhead? Here are some of the arguments used:

1. They take up valuable land.2. They are more difficult to repair.3. They are more difficult to install across roads, railways and canals.4. They are much more expensive.5. They spoil the landscape.6. 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....

M

Mr Powell 2008Index

National Grid.... Complex version...

Mr Powell 2008Index

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

2003. The amount is staggering!

Mr Powell 2008Index

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!

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.

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.

Mr Powell 2008Index

An Argument....Should power cables be underground or overhead? Here are some of the arguments used:

1. They take up valuable land.2. They are more difficult to repair.3. They are more difficult to install across roads, railways and canals.4. They are much more expensive.5. They spoil the landscape.6. 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....

H

Mr Powell 2008Index

An Argument....Should power cables be underground or overhead? Here are some of the arguments used:

1. They take up valuable land.2. They are more difficult to repair.3. They are more difficult to install across roads, railways and canals.4. They are much more expensive.5. They spoil the landscape.6. 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....

H