P1 Energy for the Home

1. P1 Energy for the Home (OCR) AGAC

2. Heat and Temperature Heat is a type of energy that will flow from a warm area to a colder one. For example… cool down This cup of coffee will ____ ____ because it is _____ ____ heat energy into the surroundings. giving out This drink (taken out of the fridge) will _____ ___ because it is _____ ___ heat energy from the surroundings. warm up taking in Words – giving out, warm up, taking in, cool down

3. Specific Heat Capacity This can be thought of as “the capacity of an object to store heat”. Consider some water: If we heat this beaker up it’s fairly clear that the amount of energy it gains depends on how much water there is and how hot it gets… Energy = mass x s.h.c x temp rise E = mcΔT s.h.c = specific heat capacity Each substance has a shc. The substances with lower shc heat up faster

4. Heating ice This flat line shows where energy is being used to push the particles further apart for evaporation. The amount of energy needed to turn 1kg of a liquid into a gas is called the Specific Latent Heat of Vaporisation L. This flat line shows where energy is being used to break bonds – this has to be done during melting. The amount of energy needed to turn 1kg of a solid into a liquid is called the Specific Latent Heat of Fusion L. Temp/OC This diagonal line shows where energy is being used to increase the temperature. The amount of energy to increase the temperature of 1Kg of water By 100C is called the specific heat capacity c Time/s

5. Latent Heat of Fusion A V 12V From the previous slide we can say that the energy needed to melt water is given by… Energy = mass x specific latent heat of fusion To work out L experimentally you could… Measure the amount of energy needed to melt 1Kg of ice VIt = mL

6. House insulation Loft insulation Cavity wall insulation Double glazing Draught excluders

7. House insulation • Which type of insulation costs the most? • Which type of insulation is the most effective? • Which type is the most “cost effective”? • Which type pays for itself after 40 years? Double glazing Loft insulation Draught excluder Double glazing

8. Efficiency Efficiency = Useful energy out Energy in x100% Efficiency is a measure of how much USEFUL energy you get out of an object from the energy you put INTO it. For example, consider a TV: Light (80J) Electrical Energy (200J) Sound (40J) Heat (?) 120 200 = 60% x100 =

9. Some examples of efficiency… • 500J of electrical energy are put into a motor. The motor converts this into 100J of movement energy. How efficient is it? • A laptop can convert 400J of electrical energy into 240J of light and sound. What is its efficiency? Where does the rest of the energy go? • A steam engine is 50% efficient. If it delivers 20,000J of movement energy how much chemical energy was put into it? 100 500 x100 =20% 240 400 = 60% x 100 40,000J

10. Conduction Conduction is all about when heat is transferred through a _____. The heat is passed on by ___________ in the molecules. These vibrations get BIGGER when the solid has more ENERGY (i.e. when it is being _______). Metals are _______ conductors than non-metals. This is because the heat is carried by free ________ that can carry the energy around the metal and give it to other electrons and ions. solid vibrations heated better electrons Words – vibrations, electrons, solid, heated, better

11. Convection Convection is all about when a gas or liquid (“fluid”) moves and carries heat with it. When the fluid is heated it _________. This means that it will become less ________ than the colder fluid around it. Because of this the warmer fluid will try to “_______” over the colder fluid, and this is why warm air rises. This is called a convection ________. This is how heat reaches us from the ___________ in this room. In CONDUCTION the heat was passed on by VIBRATIONS in a SOLID In CONVECTION the heat is passed on by the FLUID expanding, rising and TAKING THE HEAT with it expands dense float current radiators Words to use: expands, radiators, dense, heated, current, float

12. Some questions on convection… • Freezers in supermarkets are often left open to the air. Explain why the food does not melt easily. • Explain why a hot air balloon rises in the air. • Explain why an ice cube floating at the top of a drink will cool all of the drink. Cold air does not rise – it falls Heated air expands It becomes less dense than the surrounding air Ice cube melts. The cold water produced is more dense than the surrounding drink and sinks

13. Radiation An introduction… I’m cool! I’m very hot! White does not absorb as much heat- it reflects it Black ABSORBS More heat Be careful, DO not use the word “attract” heat

14. Some examples of radiation “Thermograms”

15. Some examples of radiation

16. Radiation Practical Black cools down quicker than silver

17. Radiation waves Radiation is when heat moves around in electromagnetic _________ like light does. Any hot object will emit heat radiation – the hotter it is, the more radiation it emits. This type of radiation is called __________, and too much of it will cause _________. Dark, matt colours will absorb AND emit the _____ infra-red radiation, and light, shiny colours will ________ it. The main difference with radiation is that conduction and convection could ONLY happen in solids, liquids or gases, whereas radiation will happen through an _____ _____. This is just as well, as otherwise we wouldn’t be able to get any heat from the ___. infra-red sunburn most reflect empty space Sun Words – sun, reflect, infra-red, waves, most, empty space, sunburn Anything HOT emits HEAT RADIATION – the hotter it is, the more infra red radiation it emits

18. Understanding Heat Transfer 1) Explain how and where all 3 processes of heat transfer happen in a bonfire 2) By considering how a Thermos Flask is built explain how it manages to keep hot drinks hot and cold drinks cold.

19. Understanding Heat Transfer 2 3) Car radiators are designed to help car engines lose heat. Explain how they do this. 4) Some houses have solar collectors on their roof. Explain how they work:

20. Electromagnetic Radiation E-M radiation is basically a movement of energy in the form of a wave. Some examples:

21. The Electromagnetic Spectrum High frequency, _____ wavelength Low frequency, _____ (high) wavelength γ Each type of radiation shown in the electromagnetic spectrum has a different wavelength and a different frequency: long short vacuum Each of these types travels at the same speed through a _______ (300,000,000m/s), and different wavelengths are absorbed by different surfaces (e.g. infra red is absorbed very well by _______ surfaces). This absorption may heat the material up (like infra red and ____________) or cause an alternating current (like in a __ _______). black microwaves TV aerial Words – black, microwaves, long, short, TV aerial, vacuum

22. The Electromagnetic Spectrum Type of radiation Uses Dangers Treating cancer, sterilisation Gamma rays Cell mutation X rays Medical Cell mutation UVA, UVB and UVC Sun beds Skin cancer None (unless you look at the sun) Visible light Seeing things Remote controls, heat transfer Infra red Sunburn Microwaves Satellites, phones Burns TV/radio Communications Very few

23. Refraction through a glass block: Wave slows down and bends towards the normal due to entering a more dense medium Wave speeds up and bends away from the normal due to entering a less dense medium Wave slows down but is not bent, due to entering along the normal

24. Examples of refraction

25. Refraction speed up Refraction is when waves ____ __ or slow down due to travelling in a different _________. A medium is something that waves will travel through. medium

26. Finding the Critical Angle… THE CRITICAL ANGLE 1) Ray gets refracted 2) Ray still gets refracted 4) Ray gets internally reflected 3) Ray still gets refracted (just!)

27. Uses of Total Internal Reflection Optical fibres: An optical fibre is a long, thin, _______ rod made of glass or plastic. Light is _______ reflected from one end to the other, making it possible to send ____ chunks of information transparent internally large Optical fibres can be used for _________ by sending electrical signals through the cable. The main advantage of this is a reduced ______ loss. communications signal Words – communications, internally, large, transparent, signal

28. Analogue vs. Digital + 1 - 0 Analogue signals (like talking or music) continually vary in amplitude and/or frequency Digital signals, however, are either off or on, and the information is sent in a series of pulses • There are two main advantages of digital: • More information can be sent down the same cable • Better quality, because a digital signal can be amplified without amplifying the extra noise:

29. Wireless devices The trouble with optical fibres and electrical connections is that they need wires. This is a big advantage when sending information using radio waves and microwaves. However, they have disadvantages as well...

30. Blocking reception Microwaves can be blocked by obstructions

31. Using Satellites with microwaves Microwaves are used to communicate with satellites

32. Using Radio waves Radio waves are reflected off the ionosphere (an electrically charged layer in the atmosphere)

33. Diffracting Radio Waves A low frequency radio wave can be diffracted over obstacles but some signal strength will be lost.

34. Some definitions… 1) Amplitude – this is “how high” the wave is: 2)Wavelength ()– this is the distance between two corresponding points on the wave and is measured in metres: 3) Frequency – this is how many waves pass by every second and is measured in Hertz (Hz)

35. Some definitions… Transverse waves are when the displacement is at right angles to the direction of the wave… Longitudinal waves are when the displacement is parallel to the direction of the wave…

36. The Wave Equation V  f The wave equation relates the speed of the wave to its frequency and wavelength: Wave speed (v) = frequency (f) x wavelength () in m/s in Hz in m

37. Some example wave equation questions • A water wave has a frequency of 2Hz and a wavelength of 0.3m. How fast is it moving? • A water wave travels through a pond with a speed of 1m/s and a frequency of 5Hz. What is the wavelength of the waves? • The speed of sound is 330m/s (in air). When Dave hears this sound his ear vibrates 660 times a second. What was the wavelength of the sound? • Purple light has a wavelength of around 6x10-7m and a frequency of 5x1014Hz. What is the speed of purple light? 0.6m/s 0.2m 0.5m 3x108m/s

38. Lasers Lasers produce light waves that are “coherent” – i.e. they have the same frequency and they are in phase: These two waves have different amplitudes but the same frequency and hit their peaks at the same time – they are “in phase” These two waves start opposite to each other – they are “in antiphase”

39. Using lasers in CDs This is a magnified image of the CD surface

40. The Structure of the Earth A thin crust - 10-100km thick A mantle – has the properties of a solid but it can also flow A core – made of molten nickel and iron. Outer part is liquid and inner part is solid How do we know this? These facts have all been discovered by examining seismic waves (earthquakes)

41. Seismic waves Earthquakes travel as waves through the Earth – we call them SEISMIC WAVES. There are two types: • P waves: • They are longitudinal so they cause the ground to move up and down • They can pass through solids and liquids • They go faster through more dense material • S waves: • They are transverse so they cause the ground to move from right to left • They ONLY pass through solids • They are slower than P waves • They go faster through more dense material

42. P and S waves A quick way to remember the difference: S waves are tranSverse P waves are the other type-longitudinal

43. Seismic waves S waves will only travel through a solid P waves travel through the Earth and are refracted when they pass through a medium crust Outer core Inner core mantle The paths of these waves are all curved because density is gradually changing These observations tell us 3 things about the Earth: 1) It has a thin crust, 2) it has a semi-fluid mantle where density increases with depth, 3) a core with a liquid outer part and a solid inner part.

44. Suncream It is recommended that you spend no more than 20 minutes in the sun on a sunny day. However, you could also use suncream: Ultra violet radiation in sunshine can be dangerous and cause skin cancer: Safe time = exposure time (e.g. 20 mins) x sun protection factor

45. Global Warming • Facts: • The 10 warmest years of the last century have all occurred within the last 15 years • Sea level has risen by between 12 and 24cm in the last 100 years • Rainfall has risen by 1%

46. Ozone Diagram showing the quantity of ozone in different parts of the southern hemisphere Global production of CFCs over the last 60 years