EnergySection 1: Energy stores

Ever since the universe was created the total amount of energy within it has stayed the same, this is because energy cannot be created or destroyed. We call this the law of conservation of energy. Not matter what we do we cannot make more energy or get rid of any energy. The only thing we can do is move energy around. It is this movement of energy that allows everything in our universe to happen, from a light bulb switch on to planets moving around the stars, all this is possible thanks to energy.Energy is found in stores, there are several different ways energy can be stored, these are the following:Store Definition ExampleChemical energy stored in substance to

be used laterBatteries, fossil fuels.

Thermal energy stored by the movement of particles within a substance

Elastic potential energy stored ins stretched objects

Electrostatic Energy stored by electrically charged objects

Nuclear Energy stored in atoms

Gravitational potential Energy stored in objects suspended in gravitational fields

Kinetic Energy stored in moving objects

Magnetic Energy stored in magnetic fields.

1. Give an example where we might see each store of energy?2. In your book come up with a mnemonic to help remember the stores of energy.

The amount of energy in any stores is measured in Joules (J). When anything happens, it is due to energy moving from one store to another, this happens via a pathway – a way for energy to move from store to store. For example, light from a torch will transfer energy from the torch itself and fill the thermal store of the surroundings, hence it is a pathway.

3. Give example of where we might see each of the following pathways.Pathways Example Light Torch, star, phone screen.

Sound

Heating

Electricity

Forces

A radio is a good example of an energy transfer. Energy is stored as chemical energy in the batteries, the energy is moved from the chemical store by electricity and then sound, eventually the energy is transferred to the thermal store of the radio and the surroundings.

We show this transfer as follows:

Chemical store of the battery Thermal of the radio + Thermal store of the surroundings

Energy must always be conserved so how ever much energy you have in the store at the start of the energy transfer must be the same as the total amount of energy in the stores after the transfer.

4. In your exercise book identify the energy transfers happening in the following casese.g. kettle:chemical store of fuel thermal store of the water, kettle and surrounding

a) Someone riding a bikeb) A Pendulumc) Someone firing a bow and arrow

Energy transfers can also be shown and described using the bar model below. Each bar is named after a store of energy and is shaded to show how much energy exists in the store. Remember the total energy before and after the transfer must be the same, this will be shown by having the same number of boxes shaded at the start and end.

Torch

The torch starts with most of it’s energy in the chemical store, this is in the battery. When the torch is turned on energy transfers via electricity to thermal store of the torch, the energy is finally transferred via light to the thermal store of the surroundings.

Chemical energy is stored in the batteries.

Electrical current in wires heats up radio

Sound waves heat up the surroundings

In the above example we can see the user has identified the stores then energy exists before the transfer (on the left) and the stores the energy exists in after the transfer (on the right.) This gives us a very quick overview of what ahs happened during the transfer.

5. Have a go at completing some of the energy transfer bar models yourself; use the energy transfers you write down earlier, remember to:

1. Label the bars with the stores involved in your transfer2. Make sure total energy before and after is the same3. Give a written explanation of what is happening.

Energy transfer in a kettle:

Energy transfer when someone riding a bike:

Energy transfer in a pendulum:

Energy transfer when someone fires a bow and arrow

These questions are to be answered in your exercise book.6. Name the 8 stores of energy.7. Copy and complete the following sentences:

Some people think that light is a store of energy they are wrong because…. Some people think that energy can be created or destroyed they are wrong

because….8. What is energy measured in? 9. As a car moves along chemical energy is transferred to what stores?10. On a building site a machine is used to lift a bag of sand from the ground to the

top of a building. What type of energy has the bag of sand gained? 11. What type of energy is stored in a stretched rubber band?12. When the rubber band is released what stores of energy will increase?13. Draw a bar model diagrams showing the energy transfer taking place when the

rubber band is releases.14. What type of energy store increase as a climber moves up a cliff side?15. What type of store is emptying as the climber climbs?16. A ball is thrown with 50J of kinetic energy, it hits a target which moves with 30J of

kinetic energy, how much energy goes to the thermal store of the surroundings?17. After a kettle has been boiled the water has gained 150J of energy and the

surroundings have gained 75J of energy, how much energy has the kettle transferred?

18. Draw a bar model diagram for the energy transfer above.

Session 2: Efficiency.

Not all energy is always in stores that are useful to us, any energy in a store that is not needed is known as waste energy. For example, when the chemical energy stored in the fuel is transferred to the thermal energy of a car instead of the cars kinetic store that energy is wasted. Efficiency is a way we can measure how effective a transfer is, the more energy that is transferred to a useful store the better and the higher the efficiency will be. Efficiency is measured as a percentage, 100% would mean that all the energy transferred ends up in a useful store. We use the following equation to work out efficiency:

Efficiency=useful energy output (¿Joules)total energy input (¿ Joules)

×100

Example: A light bulb will transfer 150J in one minute, 100J of this energy is used to light the bulb and 50J is used to heat up the surroundings. What is the bulbs efficiency?So we need to determine the useful output and total input then substitute these values into the equation.

Efficiency=usefulenergy output (¿Joules)total energy input (¿ Joules)

×100

Useful output = 100J

Total input = 150J

Efficiency=100150

×100=67%

19. In your exercise book write out the efficiency equation and rearrange is to get the equations for useful energy output and total energy input.

20. In a fan 250J of energy are transferred from the chemical store to the kinetic and thermal stores. The thermal store gets 100J and the kinetic store receives 150J, work out the fans efficiency.

Sankey diagrams are another way we can show the efficiency of an energy transfer. They are scaled drawings used to show the total input, useful output and wasted output.

The total input, useful output and non-useful output are indicated by the width of there arrows. These values can be worked out either by measuring the widths of each arrow and using scale or by counting the squares that make up the width of the arrows.

21. Draw a Sankey diagram for the energy transfer in the kettle from the previous question.

These need to be completed in your exercise book21. Copy and complete the following sentences:

Some people think that wasted energy disappears they are wrong because….

Some people think the lengths of the arrows in a Sankey diagram mean something they are wrong because….

22. What energy is not usefully transferred in a mobile phone?23. What energy is not usefully transferred in a kettle?24. What useful energy/energies are output from a rollercoaster being pulled up

ramp?

25. A cyclist uses 500J of energy getting up a hill, 300J of energy is transferred to the kinetic store the rest is transferred to the surrounds, what is the efficiency?

26. A bungee jumper has 3250J of gravitational potential energy, when it is dropped 500J of energy is transferred to the thermal store of the surroundings, how efficient is the transfer?

27. A ball is dropped in a vacuum, will any energy be transferred to the thermal store of the surroundings? How efficient will the transfer be.

28. A toaster is 85% efficient, it transfers 250J every minute, how much of this energy is transferred usefully?

29. A kettle is 60% efficient, it takes 600J of energy to boil the water, how much energy needs to be supplied?

30. A iron is 75% efficient, 500J is wasted, what it the total input?

31. Use the Sankey diagram on the right to work out the efficiency of the of the light.

32. Draw a Sankey diagram showing the following: Total input = 250J, useful output = 200J, wasted output = 50J.

33. A speed boat will transfer 5000J of chemical energy a second. 2000J of this will transfer to the kinetic store, the rest is wasted being transferred to thermal stores. Draw a Sankey diagram to show this and work out the speed boats efficiency.

Session 3: Thermal energy transfers.

Thermal energy is the most common store of energy found in transfers, it makes up a huge amount of the energy that exists in our universe and everyday more energy is being transferred into this store.It is possible for thermal energy to move around and how this happens depends on what medium the thermal energy is trying to be transferred through.Through solids thermal energy is transferred via conduction, in fluids (liquids and gases) thermal energy is transferred by convection and through a vacuum it’s transferred as infra-red radiation.

34. Complete the table to show which type of thermal energy transfer happens for each medium.

Medium Type of thermal energy transfer

Solid

Fluid

Vacuum

Conduction.

When a particle gains thermal energy it begins to vibrate or move faster. In a solid these particles are all lined up in neat ordered rows. So when the

temperature of a solid is raised, its particles begin to vibrate faster, as one particle vibrates faster is collides with it’s neighbouring particle causing it to vibrate faster and this happens all the way along the length of the solid – this is conduction.

This happens in both metals and non-metals but in metals we also have free electrons, these small particles are free to move in between all of the larger particles, as they gain more energy, the move faster colliding with the larger particles as they move past them, transferring some thermal energy to them. This means thermal energy transfers much fast in metal than in non-metals.

Answer these in your books.35. Draw a particle diagram for a solid and describe the motion of the particles.36. Would conduction happen faster in a metal or a non-metal?37. Draw two diagrams to show the difference between conduction in metals and non-

metals – write an explanation to go along with this.38. Would conduction happen faster in a more or less dense solid?39. Give three uses of conduction.40. Why is insulation always made from non-metals?41. What is the advantage of using a air gap in a insulated wall?

Convection.

Liquids and gases like solids are made of particles, in a liquid and a gas the particles are not held in position and so can move around. When heat rises, it does so because of convection. Convection is a process explaining how thermal energy moves through out liquids and gases, it can be broken down into simple steps.

1. A fluid is heated so its particles begin to move around faster.2. AS they move faster the particles move away from each other and the fluid

expands.3. Because the particles have moved away from each other the density of the fluid

drops. This causes it to rise above the denser fluid above it.4. As the fluid is no longer near a heat source its particles begin to lose thermal

energy and hence slow down.5. The slowing particles move closer together meaning the density goes up and the

fluid sinks below the less dense fluid beneath it.6. The process will then repeat itself.

This recurring process is known as a convection current and explains how thermal energy moves throughout a fluid.

42. Label the diagram below using the steps above to show your understanding of convection.

Answer these in your book.43. Draw a particle diagram of a liquid and a gas.44. Explain what we mean by the term density.45. Draw a particle diagrams for a low density and high density gas.46. Draw a diagram and add notes to explain how convection occurs.47. Complete the following sentence:

Some people say that particles expand during convection. This is wrong. In fact…..

48. Explain why is the heating element always at the bottom of a kettle?49. Explain why food in an open top freezer won’t defrost?50. Explain how Chinese lanterns or hot air balloons work?

Infrared radiation

Most of thermal energy on earth is transferred from the sun. The energy can’t get to us by conduction or convection as these require particles and space is a vacuum, so no particles. There is a third way, thermal energy can be transferred as a wave. Infrared radiation is a type of electromagnetic wave, meaning it needs no particles to move through. It carries thermal energy and is given off by all objects. The sun gives out huge amounts of infrared radiation which travels through space and eventually warms up our planet, making it suitable for life.

When this infrared radiation is incident on a surface, meaning it hits it, it will do one of three things, it will either reflect of the surface, be absorbed by the object or travel through the object.

Some surfaces are transparent, this means that an electromagnetic wave like

infrared will travel straight through, a window is common example of this. This is called transmission

Light, smoot, shiny surfaces will reflect any wave that hits them this includes infrared waves.

Dark, rough matt surfaces will absorb the waves the hit them, once the energy from the wave has been absorbed it is emitted back out as another infrared wave.

Infrared radiation investigation.Using different coloured surface cans we can test how well the different surfaces reflect or absorb infrared radiation. Take a silver surface and black matt surfaced can and fill them with boiling water, take a starting temperature then allow the water to cool for 5 minutes and retake the temperature. The results would show that the black can will have cooled by the most.Type of can Initial temperature /

OCFinal temperature / OC Chane in

temperature / OC

Answer the following questions about the infrared radiation investigation.

51. What is the independent variable?52. What is the dependant variable?53. What are the control variables? Give 3 examples.54. Explain the results of the investigation.

Insulation.

A large number of products are required to either keep things or cold, a thermos is a good example of this. These products need to use insulators to stop thermal energy transferring by conduction, convection or radiation. Insulators make use of materials that are poor conductors of heat, things like plastic, trapped air or vacuums are most commonly used.

This diagram of a thermos shows us how these different ideas are put into practise.

51. In your exercise book explain how each part of the thermos is used to help with insulation.

52. What type of wave in infrared radiation?53. What type of thermal transfer can travel through a:

Solid? Liquid? Gas? Vacuum?

54. Which type of surface will infrared radiation travel through?55. Which type of surface will infrared reflect off?56. Which type of surface will absorb infrared radiation?57. Finish the following sentence:

Some people think that dark, matt surfaces on absorb infrared radiation they are wrong because…..

58. Explain the difference between conduction in a metal and a non-metal.59. Use the three different types of thermal energy transfers to explain how water is

heated in a metal pan above a fire.60. Explain why fridges are made of white plastic.61. Explain why a lid will help to insulate a bottle.62. Explain how cavity wall insulation works.

Session 4: Power, energy and cost.

It is important to know how much energy is transferred by a device every second, this will help us to know which device uses more electricity and how much devices will cost us to run.

The amount of energy transferred per second is known as power and is measured in Watts. Power can be calculated using the following formula:

Power(Watts)=Energy transferrec (Joules)Timetake(seconds )

Converting time:1 minute 60 seconds (x 60)1 hour 60 minutes (x 60)

1 hour 3600 seconds (x 3600)1 second 0.00028 hour (÷ 3600)1 minute 0.017 hours (÷ 60)

Example: A kettle transfers 5000J to the thermal store in 2 minutes, what tis the power of the kettle.

Convert 2 minutes into seconds: 2 x 60 = 120 s

Power(Watts)=Energy transferrec (Joules)Timetake(seconds )

Power = 5000 ÷ 120Power = 42 W

63. Copy the formula into you exercise book and rearrange it to make energy transferred and time taken the products.

64. Use the power equation fill in the blanks in the table, show your working in your exercise book:

There is a large cost in producing electricity that must be covered by the consumer. To cover these costs electricity companies, charge people for the electricity they use. They do this by measuring the energy a household uses per month, Joules are too small a unit to measure this much energy, a house will use over a billion joules of energy a month. Instead the following formula is used to work out the energy used by a household in Kilowatt hours KWh.

Energy (KWh )=Power (KW )×Time (hours)

Example: A 42W kettle takes 2 minutes to boil, how much energy is transferred?

Convert Watts into Kilowatts: 421000

= 0.042 KW

Convert minutes into hours: 260

= 0.03 hours

Energy = 0.042 x 0.03 = 0.00126 KWh

Energy transferred (J)

Time taken for transfer (s)

Power (W)

100 1

200 2

4000 1000

20 2

30 175

20 2000

Using the energy transferred in KWh the electricity companies can work out how much to charge using the following formula:

Cost=Price× Energyused

The price will be set by the electricity company and is how much is charged for each KWh used, e.g 13 pence per KWh.

65. What is the power of a bulb that transfers 300J of energy every 30 seconds?66. What is the power of a television that transfers 6750J of energy every 45 seconds?67. A toaster runs for 3 minutes. During this time, it transfers 216,000J of energy.

What is the toaster’s power?68. Toaster 1 has a power rating of 700W and toaster 2 has a power rating of 900W,

which microwave will heat up my dinner fastest and why?69. A dishwasher transfers 2,160,000J in 30 minutes. What is its power in kW?70. My washing machine’s wash cycle takes 30 mins. During each wash cycle, it

transfers 900,000J of energy. What power rating does my washing machine have?71. The play station has been on for 3 hours this evening. During this time, it

transferred 1,782,000J of energy. What is the power rating of the play station?72. How many kiloWatts is 2000 W?73. How many kiloWatts is 500 W?74. If I use a 3 kW oven for 2 hours, how much electrical energy do I use?75. How much electrical energy is used by a 2 kW appliance in 5 hours?76. A 5000 W washing machine is used for 6 hours, how much electrical energy is

transferred?77. A 0.5 kW light bulb is left on for 10 hours. How much electrical energy is used?78. A 2000W hairdryer is used for 30 minutes. How much electrical energy is used?

Session 5: Generating electricity.

Electricity can be generated in a number of different ways using a number of different sources. These are broken into two groups; renewable and non-renewable. Non-renewable energy comes from sources that cannot easily be replenished once used, these include fossil fuels (coal, oil and gas) and nuclear power.Renewable energy sources are easy to replace or replenish, these include sources such as solar power and hydroelectricity.

Non-renewable sources.

Fossil fuels.

Fossil fuels are produced when living material buried deep underground for millions of years breakdown forming either coal, oil or gas. Coal is produced by plant life undergoing this process whereas oil and gas originate from animal life.To produce electricity these fuels are burnt in a power station, the heat is used to boil water to produce steam. This steam is used to spin a turbine which in turn runs a electricity generator. In terms of energy transfer the chemical store of the fuel is transferred to the thermal store of the water and steam, this transfers to the kinetic store of the turbine which eventually transfers to the electrostatic store in the generator.

79. Label the diagram to explain what is happening at points 1, 2, 3 and 4.Burning these fuels releases a huge amount of energy but unfortunately many of the products produced during the combustion of the fuels are carbon-based gases such as carbon dioxide and carbon monoxide. These carbon products would have stayed trapped away in the fossil fuel indefinitely, but burning the fuel releases them. These gases are known as greenhouse gases and are partly responsible for global warming.Nuclear

Nuclear power uses energy released when atoms a broken apart, a process known as nuclear fission, this process releases lots of energy but leaves us with radioactive waste.

Renewable resources.

Biofuel

Plant matter such as wood and vegetable oils can be used in the same way fossil fuels are to produce electricity, these don’t release as much energy as fossil fuels but the carbon emissions have much less impact than those released from coal, oil and gas.

Solar

Solar power uses photovoltaic cells to harness energy from light and other waves given off by the sun, this energy is free but is not always readily available.Wind

Wind power uses kinetic energy stored in the wind to spin a turbine and run a generator, this like solar power is free, but is not always viable, the wind turbines also pose a threat to bird life and some think they ruin the aesthetics of the landscape.

Wave

Wind across the oceans generate waves, the minetic energy in these waves can be used to generate electricity, this again is free but not reliable. Like wind turbine wave power generators pose a threat to wildlife.Tidal

The moons orbit around the planet causes tidal patterns in our oceans, the slow moving of water in and out from our shores. This movement can be used to genertate electricity. Due to the predictability of the tides, this source is very reliable, but similarly to wave power does threaten wildlife.Geothermal

The core of our planets releases a vast amount of thermal energy, we only need to dig down 10km to find temperature hot enough to boil water, this steam can be used to generate electricity just like in a fossil fuel power station. This form of power is reliable but has big impact on the local environment as large bore holes need to be dug.

Hydroelectric

Moving water is a common source of power, in this case water trapped behind a damn can be released at any time to help produce electricity. The water can be pumped back up into a reservoir to be used again at any time. This method of generating electricity if hugely effective but like others does have a big impact on the local environment, in the worst cases valleys have had to be flooded in order to create reservoirs. Apart from being renewable one the biggest advantages of these energy sources is that they don’t produce any pollution.

80. Use the information above the fill in this table.

Name of renewable energy source

Detail Advantages Disadvantage

SolarCollect energy being transferred by sunlight to produce electricity.

Wind Is free to run and is renewable.

Wave Is unreliable and can herm sea life

TidalUses the movement of the ocean, caused by the moon, to generate electricity.

Biomass Does not produce a lot of electricity.

GeothermalIs reliable and the energy is free, no fuel needed.

Hydroelectric

Uses the movement of water due to gravity to generate electricity.

Fossil Fuels(Coal, Oil and Gas)

Causes lots of pollution, fuels are expensive.

81. Finish the following sentences: Some people think that a non-renewable energy source is one that will run

out, they are wrong because…… Some people think that nuclear power is partly responsible for global

warming they are wrong because….. Some people think that wave power is reliable they are wrong because…..

82. As water flows from the top to the bottom lake it turns a turbine coupled to a generator that produces electricity.

What is the energy transformation that takes place as the water flows?A Electrical energy to kinetic energy.B Gravitational potential energy to kinetic energy.C Kinetic energy to gravitational potential energy.D Kinetic energy to heat energy.

83. Where does geothermal energy come from?A Radioactive processes in nuclear power stations.B Radioactive processes within the Earth.C The decay of organic material.D The movement of the tides.

84. Renewable energy sources can be used to generate electricity. However these sources are not always available.

Match words from the list with the numbers 1 to 4 in the table.A hydroelectric scheme ……….B solar cells ……….C tidal barrage ……….D wind farm ……….

Renewable energy source

Source is available to generate electricity …

1 only during the daylight

2 only when the weather is suitable

3 only during certain periods of the day and night

4 usually whenever it is needed

85. Wind energy, waves, tides, falling water and solar energy can all be used as energysources to generate electricity.

(a) What do all these energy sources have in common?A They are available at any time of the day or night.B They are non-renewable energy sources.C They do not affect wildlife.D They do not cause any sort of pollution.

(b) Which of these energy sources is most appropriate to generate electricity to run a well in a remote African village?A falling water

B solar energyC tidesD waves(c) Which of these energy sources is most likely to produce noise pollution when

used to generate electricity? A solar energyB tidesC wavesD wind energy

(d) Which of these energy sources is least likely to be associated with damaging wildlife or the habitat of wildlife when used to generate electricity?

A falling waterB tidesC wavesD wind energy

86. What is the unit for energy? 87. What are the 8 energy stores?88. Which store fills when energy is ‘wasted’? 89. What is a fuel?90. Why does the Bunsen burner flame release more energy when the hole in the

Bunsen is open?91. Which method of heat transfer occurs when particles collide with each other?92. Why do regions of hot liquids and gases rise?93. Which colour absorbs and emits the most Infrared radiation?94. Why are hot food takeaway containers silver or white?95. What is the equation to calculate power?96. Which unit is used for power?97. What is 1 watt equal to in terms of joules?98. What is a fossil fuel?99. What does the term ‘renewable’ mean?

100. How do insulators help us save money?101. Look at the Sankey diagram. Calculate the efficiency of the light.

Incorrect statement Correct statement

Heat rises

When solids are heated, the particles expand

Black objects get hotter because

they attract heat

Two control variables when testing foods to see how much

energy they release are:Amount of food

Amount of water in test tube

A fuel is something that produces energy when it burns

When we heat a solid, the particles start to vibrate

Insulators stop energy transfers

Burning fossil fuels releases pollution