Energy for the Home

1. Energy for the Home (OCR Gateway) W Richards

2. P1a – Heating Houses

3. Particle theory revision Particle theory is all about explaining the properties of solids, liquids and gases by looking at what the particles do. SOLIDS In a solid the particles ______ around a _____ position. There is a ______ force of attraction between each particle and they are very _____ together Words – strong, close, vibrate, fixed “Temperature” is simply a way of measuring how fast these particles are vibrating.

4. LIQUIDS In a liquid the particles are _____ together but can move in any direction. They won’t keep a _____ shape like _____ do. GASES In a gas the particles are very far apart and move _____ in all directions. They often ______ with each other and because they are far apart they can be easily _______. Words – fixed, collide, quickly, close, squashed, solids

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

6. Understanding Thermograms

7. 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 αmass x temperature rise Energy = mass x s.h.c x temp E = mcΔT

8. Specific Heat Capacity A V 12V How can we do this experimentally? E = VIt and E = mcΔT Possible errors with this experiment: • Temperature throughout the liquid should be the same • Solution: • Heat is lost to the surroundings • Solution(s):

9. 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 Time/s

10. 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… VIt = mL

11. P1b – Keeping homes warm

12. 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. Heating a non-metal Heating a metal Words – vibrations, electrons, solid, heated, better

13. 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 Words to use: expands, radiators, dense, heated, current, float

14. 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.

15. Radiation An introduction… I’m cool! I’m very hot!

16. Some examples of radiation “Thermograms”

17. Some examples of radiation

18. Radiation Practical

19. Radiation 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 ___. 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

20. 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.

21. 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:

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

23. Types of House Insulation Loft insulation Double glazing Cavity wall insulation What else would this house benefit from? How do these forms of insulation help?

24. Heat Sources and Heat Sinks In general, anything that gives out heat (e.g. this house) is called a “heat source”. The term “heat sink” refers to the place the source’s heat will be transferred to, and it’s usually an object so large that it’s temperature won’t change.

25. 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?

26. 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 (?)

27. Some examples of efficiency… • 5000J 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?

28. Energy Transfer (“Sankey”) diagrams Consider a light bulb. Let’s say that the bulb runs on 100 watts (100 joules per second) and transfers 20 joules per second into light and the rest into heat. Draw this as a diagram: “Input” energy “Output” energy 20 J/s light energy 100 J/s electrical energy 80 J/s heat energy (given to the surroundings)

29. Example questions Consider a kettle: Consider a computer: 2000 J/s electrical energy 150 J/s electrical energy 20 J/s wasted heat Wasted heat Heat to water Useful light and sound 10 J/s wasted sound Sound energy • Work out each energy value. • What is the kettle’s efficiency? • How much energy is converted into useful energy? • What is the computer’s efficiency?

30. P1c A Spectrum of Waves

31. An introduction to Waves

32. Some definitions… “Crest” “Trough” 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)

33. 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

34. 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

35. Reflection Angle of incidence = Angle of reflection Normal Reflected ray Incident ray Angle of reflection Angle of incidence Mirror

36. 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

38. Refraction Refraction is when waves ____ __ or slow down due to travelling in a different _________. A medium is something that waves will travel through. When a pen is placed in water it looks like this: In this case the light rays are slowed down by the water and are _____, causing the pen to look odd. The two mediums in this example are ______ and _______. Words – speed up, water, air, bent, medium

39. Wave diagrams 1) Reflection 2) Refraction 3) Refraction 4) Diffraction

40. Diffraction More diffraction if the size of the gap is similar to the wavelength More diffraction if wavelength is increased (or frequency decreased)

41. Limiting Effects of Diffraction The effect of diffraction causes microscopes and telescopes to naturally have a limit of what they can “resolve”. This is the image seen by a telescope when pointing at a star – the rings are caused by diffraction effects and they will cause difficulty when viewing stars that are near each other.

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

43. 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: 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 __ _______). Words – black, microwaves, long, short, TV aerial, vacuum

44. 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

45. P1d – Light and Lasers

46. Sending Signals What are the advantages and disadvantages of using sound and light? Ever since the dawn of humanity, humans have been thinking of effective and fast ways of sending signals:

47. Using Light to send Signals Morse code is a signal that consists of short bursts and long bursts and therefore is classed as a “digital” signal as each message can be one of only two forms. These signals could be relayed between ships over long distances. Modern signals can be sent by radio or electric signals instead. What are the advantages of these methods over using light?

48. 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!)

49. 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 Optical fibres can be used for _________ by sending electrical signals through the cable. The main advantage of this is a reduced ______ loss. Words – communications, internally, large, transparent, signal

50. 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” Lasers produce an intense, coherent beam of light where the waves all have the same frequency (i.e. they’re the same colour), they are all in phase and they have a low divergence (they don’t spread out). Because of these properties lasers can be used for surgery, cutting materials and weapon guidance.