Kinetic Theory. Energy. Transfers and Efficiency. The National Grid

Transcription

1 AQA P1 Revision

2 Infrared Radiation Heating and Insulating Buildings Kinetic Theory Energy Transfers and Efficiency Energy Transfer by Heating Transferring Electrical Energy Generating Electricity The National Grid Waves Reflection Sound Red Shift and the Big Bang Theory

3 Infrared Radiation a) All objects emit and absorb infrared radiation. b) The hotter an object is the more infrared radiation it radiates in a given time. c) Dark, matt surfaces are good absorbers and good emitters of infrared radiation. d) Light, shiny surfaces are poor absorbers and poor emitters of infrared radiation. e) Light, shiny surfaces are good reflectors of infrared radiation.

4 Emitting Infrared Radiation All objects emit (give out) some thermal radiation. Certain surfaces are better at emitting thermal radiation than others. best emitter worst emitter matt black white silver Matt black surfaces are the best emitters of radiation. Shiny surfaces are the worst emitters of radiation. Which type of kettle would cool down faster: a black kettle or a shiny metallic kettle?

5 Absorbing Infrared Radiation Infrared waves heat objects that absorb (take in) them. best emitter matt black best absorber white worst emitter silver worst absorber Matt black surfaces are the best absorbers of radiation. Shiny surfaces are the worst emitters because they reflect most of the radiation away. Why are solar panels that are used for heating water covered in a black outer layer?

6 Infrared Radiation Exam Questions

7 Kinetic Theory a) The use of kinetic theory to explain the different states of matter. b) The particles of solids, liquids and gases have different amounts of energy.

8 Kinetic Theory As you heat a substance, the heat energy is transferred to the particles in the substance as kinetic energy. This causes the particles to move further apart, decreasing the density of the substance.

9 Kinetic Theory A loss of heat energy will cause the opposite effect.

10 Kinetic Theory Exam Questions

11 Energy Transfer by Heating a) The transfer of energy by conduction, convection, evaporation and condensation involves particles, and how this transfer takes place. b) The factors that affect the rate of evaporation and condensation. c) The rate at which an object transfers energy by heating depends on: surface area and volume the material from which the object is made the nature of the surface with which the object is in contact. d) The bigger the temperature difference between an object and its surroundings, the faster the rate at which energy is transferred by heating.

12 Energy Transfer by Heating solid liquid gas Particles that are very close together can transfer heat energy as they vibrate. This type of heat transfer is called conduction. Conduction is the method of heat transfer in solids but not liquids and gases.

13 Energy Transfer by Heating Warmer regions of a fluid are more dense than cooler regions of the same fluid. The warmer regions will rise because they are more dense. The cooler regions will sink as they are less dense. This is how heat transfer takes place in fluids and is called convection. The steady flow between the warm and cool sections of a fluid, such as air or water, is called a convection current.

14 Energy Transfer by Heating The Earth is warmed by heat energy from the Sun. How does this heat energy travel from the Sun to the Earth? infrared waves There are no particles between the Sun and the Earth, so the heat cannot travel by conduction or by convection. The heat travels to Earth by infrared waves. These are similar to light waves and are able to travel through empty space.

15 Energy Transfer by Heating How is a vacuum flask able to keep hot drinks hot and cold drinks cold? 2. The plastic (or cork) lid is an insulator and the screw top prevents convection currents escaping from the flask. 1. There is a vacuum between two layers of glass or steel, which prevents heat leaving or entering by conduction. 3. The walls have silvery surfaces, which prevent heat leaving or entering by radiation.

16 Energy Transfer by Heating Heat loss through evaporation.

17 Energy Transfer by Heating Quick Quiz

18 Energy Transfer by Heating Exam Questions

19 Energy Transfer by Heating Exam Questions

20 Heating and Insulating Buildings a) U-values measure how effective a material is as an insulator. b) The lower the U-value, the better the material is as an insulator. c) Solar panels may contain water that is heated by radiation from the Sun. This water may then be used to heat buildings or provide domestic hot water. d) The specific heat capacity of a substance is the amount of energy required to change the temperature of one kilogram of the substance by one degree Celsius. Energy transferred = mass x specific heat capacity x temperature change

21 Heating and Insulating Buildings A thermogram shows the distribution of heat over the surface of a house. It highlights where heat is being lost. The white, yellow and red areas are the warmest, so these are the worst insulated parts of the house. The blue and green areas are the coolest, so these are the best insulated parts of the house.

22 Heating and Insulating Buildings

23 Heating and Insulating Buildings The specific heat capacity of a material is the amount of energy required to raise 1 kg of the material by 1 C. It can be used to work out how much energy is needed to raise the temperature of a material by a certain amount: energy specific heat = mass x capacity x temperature change Energy is measured in joules (J). Mass is measured in kilograms (kg). Temperature change is measured in C. Specific heat capacity is measured in J/kg C.

24 Heating and Insulating Buildings Using the specific heat capacity of water (4200 J/kg C), how much energy is needed to increase the temperature of 600 g of water by 80 C in a kettle? Note: mass = 600 g = 0.6 kg energy specific heat = mass x capacity x temperature change energy = 0.6 x 4200 x 80 = J

25 Heating and Insulating Buildings Exam Questions

26 Energy Transfers and Efficiency a) Energy can be transferred usefully, stored, or dissipated, but cannot be created or destroyed. b) When energy is transferred only part of it may be usefully transferred, the rest is wasted. c) Wasted energy is eventually transferred to the surroundings, which become warmer. The wasted energy becomes increasingly spread out and so becomes less useful. d) To calculate the efficiency of a device using:

27 Energy Transfers and Efficiency The energy efficiency of a device can be calculated using this formula: energy efficiency = useful output energy total input energy Useful energy is measured in joules (J). Total energy is measured in joules (J). Energy efficiency does not have any units. It is a number between 0 and 1 which can be converted into a percentage by multiplying by 100.

28 Energy Transfers and Efficiency All the energy transfers (useful and wasted) that are associated with a device can be represented by a Sankey diagram. A Sankey diagram uses arrows to represent all the output energies. The thickness of each arrow is proportional to the amount of energy involved at that stage. 100 J electrical energy (input) Filament light bulb 90 J heat energy (wasted) 10 J light energy (output) Energy efficient light bulb 20 J 10 J electrical light energy energy (input) 10 J (output) heat energy (wasted)

29 Energy Transfers and Efficiency Exam Questions

30 Transferring Electrical Energy a) Examples of energy transfers that everyday electrical appliances are designed to bring about. b) The amount of energy an appliance transfers depends on how long the appliance is switched on and its power. c) To calculate the amount of energy transferred from the mains using: Energy transferred = power x time d) To calculate the cost of mains electricity given the cost per kilowatt-hour.

31 Transferring Electrical Energy The amount of electrical energy (i.e. the amount of electricity) used by an appliance depends on its power and how long the electricity is used for. electrical energy = power x time Power is measured in kilowatts (kw) and the time is measured in hours (h), so what are the units of electricity measured in? 1 unit of electricity = 1 unit of electrical energy = 1 kilowatt hour (kwh) Example: How many units of electricity is 17.6 kwh? 17.6 units

32 Transferring Electrical Energy Electricity costs money, which is why every home has an electricity meter. The meter records how much electricity is used in a house in units of electrical energy. The units of electrical energy are called kilowatt hours (kwh). The cost of an electricity bill is calculated from the number of units used.

33 Transferring Electrical Energy The cost of electricity is the number of units of electrical energy multiplied by the cost per unit. cost = number of units x cost per unit Example: How much would 10 units of electricity cost at a price of 9p per unit? cost = 10 units x 9 p/unit = 90 p

34 Transferring Electrical Energy A kettle uses 45.2 kwh of energy. If electricity costs 10 p per unit, how much does it cost to use the kettle? Number of units: number of units of electricity = number of kilowatt hours = 45.2 units Cost of electricity: cost = number of units x cost per unit = 45.2 units x 10 p / unit = 452 p or 4.52

35 Transferring Electrical Energy Exam Questions

36 Transferring Electrical Energy Exam Questions

37 Generating Electricity a) In some power stations an energy source is used to heat water. The steam produced drives a turbine that is coupled to an electrical generator. Energy sources include: the fossil fuels (coal, oil and gas) which are burned to heat water or air uranium and plutonium, when energy from nuclear fission is used to heat water biofuels that can be burned to heat water. b) Water and wind can be used to drive turbines directly. c) Electricity can be produced directly from the Sun s radiation. d) In some volcanic areas hot water and steam rise to the surface. The steam can be tapped and used to drive turbines. This is known as geothermal energy. e) Small-scale production of electricity may be useful in some areas and for some uses, e.g. hydroelectricity in remote areas and solar cells for roadside signs. f) Using different energy resources has different effects on the environment. These effects include: the release of substances into the atmosphere, the production of waste materials, noise and visual pollution, the destruction of wildlife habitats.

38 Generating Electricity Energy resources can be classified into two groups. Renewable Non-renewable Renewable energy resources can be replaced or regenerated and will never run out (at least not for a very long time). Examples: wind and solar. Non-renewable energy resources will eventually run out once used they cannot be used again. Examples: coal and oil.

39 Generating Electricity

40 Generating Electricity

41 Generating Electricity Exam Questions

42 Generating Electricity Exam Questions

43 The National Grid a) Electricity is distributed from power stations to consumers along the National Grid. b) For a given power increasing the voltage reduces the current required and this reduces the energy losses in the cables. c) The uses of step-up and step-down transformers in the National Grid.

44 The National Grid Power station Step up transformer Step down transformer Homes The voltage is altered in The National Grid with the use of step-up and step-down transformers. The voltage is stepped up when it leaves the power station to reduce the current - this reduces the amount of energy loss The voltage is then stepped down before it reaches our homes

45 The National Grid Exam Questions

46 Waves a) Waves transfer energy. b) Waves may be either transverse or longitudinal. c) Electromagnetic waves are transverse, sound waves are longitudinal and mechanical waves may be either transverse or longitudinal. d) All types of electromagnetic waves travel at the same speed through a vacuum (space). e) Electromagnetic waves form a continuous spectrum. f) Longitudinal waves show areas of compression and rarefaction. g) Waves can be reflected, refracted and diffracted. h) Waves undergo a change of direction when they are refracted at an interface. i) The terms frequency, wavelength and amplitude. j) All waves obey the wave equation: v = f x k) Radio waves, microwaves, infrared and visible light can be used for communication.

47 Transverse Waves Vibrations Vibrations Wave Direction The vibrations are at 90 O or right angles to the direction of the waves.

48 Transverse Waves Certain parts of a transverse wave have special names. The high points of a transverse wave are called peaks and the low points of a transverse wave are called troughs. peak trough

49 Transverse Waves The wavelength of any wave is the distance between two matching points on neighbouring waves. wavelength wavelength wavelength The wavelength is the same whichever two matching points are used to measure this distance. The symbol used to represent wavelength is.

50 Transverse Waves The amplitude of any wave is the maximum distance a point moves from its rest position. amplitude amplitude The amplitude of a transverse wave is the height of a peak or trough from the wave s rest position of the wave. The larger the amplitude, the greater the energy of the wave.

51 Transverse Waves The frequency is the number of waves passing any point each second. frequency = number of waves past a point / time frequency is measured in hertz (Hz) 1 wave per second = 1 Hz If this set of transverse waves pass a point in one second, what is the frequency? 4 Hz

52 Longitudinal Waves Vibrations Wave Direction The vibrations are parallel to the direction of the waves.

53 Longitudinal Waves Where the particles in a longitudinal wave bunch together are called compressions, where they spread out are called rarefactions.

54 Longitudinal Waves The wavelength of a longitudinal wave is measured from one compression to another, or one rarefaction to another. wavelength wavelength

55 Waves For any set of waves, the wave speed (v) can be calculated from the frequency (f) and wavelength ( ) using this formula: wave speed = frequency x wavelength v = f x What are the units of speed, frequency and wavelength? Wave speed is measured in metres per second (m/s). Frequency is measured in hertz (Hz). Wavelength is measured in metres (m).

56 Waves These waves are travelling across the surface of a pond. The length of each wave is 0.25 m. Two waves pass the duck each second, so the frequency is 2 Hz. This means that the waves travel 0.5 m each second, so the speed of the waves is 0.5 m/s. From this example, the connection between speed, frequency and wavelength is: speed = frequency x wavelength 0.5 m/s = 2 Hz x 0.25 m

57 Waves Exam Questions

58 Waves Exam Questions

59 Reflection a) The normal is a construction line perpendicular to the reflecting surface at the point of incidence b) The angle of incidence is equal to the angle of reflection. c) The image produced in a plane mirror is virtual, upright and laterally inverted.

60 A plane mirror reflects light regularly so it produces a clear image, which is the same size as the object. The image appears the same distance behind the mirror as the object is in front of it. Reflection What is different about the image compared to the object? When an object is reflected in a plane mirror, left appears as right and right appears as left. This type of reversal is called lateral inversion.

61 Reflection Exam Questions

62 Sound a) Sound waves are longitudinal waves and cause vibrations in a medium, which are detected as sound. b) The pitch of a sound is determined by its frequency and loudness by its amplitude. c) Echoes are reflections of sounds.

63 Sound Sound waves can be studied with this type of equipment. loudspeaker oscilloscope signal generator A loudspeaker converts signals from the signal generator into sound waves. A signal generator produces different types of signals. An oscilloscope shows wave patterns and allows us to see sound.

64 Sound A sound can be quiet or loud. quiet sound loud sound On an oscilloscope trace, the loudness of a sound is shown by the height of the wave. This is called the amplitude. Which word should be crossed out in this sentence? The larger the amplitude of the wave on the trace, the louder/quieter the sound.

65 Sound Which trace represents the loudest sound? A Sound A is the loudest. B Sound A has the largest amplitude (i.e. the tallest waves), so it is the loudest of these two sounds.

66 Sound A sound can be high or low this is the pitch of the sound. low pitch sound high pitch sound On an oscilloscope trace, the pitch of a sound is shown by how many waves there are. This is called the frequency. Which word should be crossed out in this sentence? The greater the number of waves across the oscilloscope trace, the lower/higher the frequency and pitch.

67 Sound Which trace represents the sound with the highest pitch? A Sound B has the highest pitch. B Sound B has the most number of waves across the oscilloscope it has the highest frequency and so has the highest pitch.

68 Sound What happens when a sound wave meets a hard flat surface? The sound wave is reflected back from the surface. This is called an echo.

69 Sound Exam Questions

70 Red Shift and the Big Bang Theory a) If a wave source is moving relative to an observer there will be a change in the observed wavelength and frequency. This is known as the Doppler effect. b) There is an observed increase in the wavelength of light from most distant galaxies. The further away the galaxies are, the faster they are moving, and the bigger the observed increase in wavelength. This effect is called red-shift. c) How the observed red-shift provides evidence that the universe is expanding and supports the Big Bang theory (that the universe began from a very small initial point). d) Cosmic microwave background radiation (CMBR) is a form of electromagnetic radiation filling the universe. It comes from radiation that was present shortly after the beginning of the universe. e) The Big Bang theory is currently the only theory that can explain the existence of CMBR.

71 Red Shift and the Big Bang Theory The Doppler effect means that sound moving away from an observer appears to be lower in frequency. The same thing happens with light from distant galaxies, which appears to be shifted towards the low frequency, red end of the spectrum. This means the distant galaxies must be moving away from the Earth. It has also been observed that the further away a galaxy is, the greater the amount of red shift. This means that very distant galaxies must be moving faster than near, all of which is evidence for the Big Bang theory.

72 Red Shift and the Big Bang Theory The observation of red shift is a key piece of evidence for the Big Bang theory about the origin of the Universe. This states that the Universe began with a colossal explosion 13,700 million years ago and has been expanding ever since. The other key piece of evidence for the Big Bang theory is cosmic microwave background radiation (CMBR). CMBR is radiation remaining from the Big Bang explosion and fills the whole of the Universe.

73 Red Shift and the Big Bang Theory The Big Bang is the most widely recognised scientific theory on how the Universe began. It states that the Universe began from a very small, very dense and very hot initial point. It burst outwards in a great explosion, and all matter and space was created in the Big Bang. It is even thought that this was the moment when time began.

74 Red Shift and the Big Bang Theory The first piece of evidence for the Big Bang is from data collected on red-shift. Red-shift shows us that galaxies which are furthest away from us are moving faster than galaxies closer to us. The galaxies are a bit like coloured sparks from an exploding firework. The sparks moving fastest travel the furthest. If you could run time backward you would see the sparks all starting in one point. The same is true for galaxies.

75 Red Shift and the Big Bang Theory In the 1960s two scientists called Wilson and Penzias noticed that a form of microwave radiation was affecting their readings. The electromagnetic radiation was everywhere and is now called cosmic microwave background radiation (CMBR). CMBR is explained as being heat left over from the Big Bang. As the Universe exploded, it cooled and the radiation was stretched out. Today this radiation is in the microwave region of the electromagnetic spectrum

76 Red Shift and the BBT Exam Questions

77 Red Shift and the BBT Exam Questions