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02 May 2017 Heat transfer Evaporation Infrared Radiation Generating Electricity Particles Heating/ Insulation Efficiency EM Spectrum Red-shift Electrical Energy Waves Formulae Big Bang How science works Interpreting graphs Checking answers 02 May 2017 Energy transfer by heating • 3 methods – conduction, convection, radiation • The bigger the temperature difference between an object and its surroundings, the faster the rate at which energy is transferred by heating. • Rate of transfer of energy depends on surface area and volume, object materials, surfaces. Back 02 May 2017 Infrared Radiation • All objects emit and absorb infrared • The hotter an object is, the more IR it emits in a given time (time is important!) • Dark, matt surfaces – good absorbers, good emitters (this means that a dark, matt object will heat up faster or cool down faster than a light, shiny one) • Light, shiny surfaces – poor absorbers, poor emitters, good reflectors. Back Conduction, convection, evaporation and condensation all transfer energy, and all involve particles in their theories. Particles In an object, the more kinetic energy the particles have, the hotter the object is. Convection Takes place in liquids and gases. When a liquid or gas gets hotter, the particles have more KE they move around more, making the liquid or gas less dense. Therefore, hot liquids or gases will rise above cooler liquids or gases. (HEAT DOES NOT RISE, HOT 02 May 2017 Conduction All to do with particles banging into each other and passing on KE. Metals have free electrons which can also pass on KE, making metals excellent conductors. The arrangement of particles in a substance determine how good a conductor it is. LIQUIDS AND GASES DO!!) Particle arrangements: Solid – fixed in place, least amount of KE but still some movement Liquid – some fixed arrangement, free to slide over each other, more KE than solid Gas – free to move about randomly, no fixed arrangement, lots of KE Back Evaporation Particles in a liquid are held together by forces The particles need lots of kinetic energy to overcome these forces So your skin is losing energy through heating the particles and it will feel colder. If particles are leaving the liquid on your skin through evaporation, they are taking kinetic energy with them. 02 May 2017 Particles can gain kinetic energy through heating but that energy has to come from somewhere Liquids on your skin get the energy they need for evaporation from your skin. The average kinetic energy of the liquid on your skin has dropped. Back Heating and Insulation Insulation materials aim to reduce energy transfer by heating – they may reduce conduction, convection, and radiation. 02 May 2017 New heating systems or insulation for a house cost money. The payback time of an investment tells you how long it will take to get your money back based on how much the investment saves you. Payback time = initial investment saving per year Insulation materials for homes (including double glazing) are often given a U-value. This is a measure of how effective the insulator is. The lower the Uvalue, the better the material is as an insulator. Liquids on your skin get the energy they need for evaporation from your skin. Solar panels sometimes contain water that is heated by the Sun. The pipes in a solar panel are often black. The hot water can be used for heating. Back Efficiency 02 May 2017 • Two formulae (you’ll be given both) • Efficiency = useful energy out (x 100%) total energy in • Efficiency = useful power out (x 100%) total power in • You might need to rearrange these and put in the numbers. • Answers can be given either as a percentage (e.g. 30%) or as a decimal (0.3) DO NOT combine these (e.g. 0.3%) Efficiency 02 May 2017 • Sankey diagrams are often used to show efficiency • Efficient: Most energy is transferred to a useful form. • Not efficient: The ratio of useful energy transferred to total energy in gives you the efficiency of the machine represented by the Sankey diagram. Most energy is transferred to a nonuseful form – it is wasted. Back Generating Electricity 02 May 2017 Power stations heat Heat can be Water and wind can water to make generated by: drive a turbine directly burning fossil fuels (no need for heating) steam steam power nuclear fissionstations still turns a turbine At night, the turbine spins a burning biofuels Fewer people generate electricity. The Sun’s energy can generator be used to generate use electricity at night (they’re Different methods electricity (either by Small-scale asleep…) of have of electricity sogenerating the supply heating water or generation is useful different effects on is much the greater than the demand. directly) in remote areas. atmosphere National grid – a grid of Step-up transformer voltage up, Electricity companies can therefore cables and transformers current down lower current means sell electricity less during theenergy transferring electrical less for heating in cables less energy around the country wasted in the cables night. Step-down transformer voltage down, current up voltage is stepped down to a level which is safe to use in homes, factories, etc. Back Electrical Energy 02 May 2017 There are a few formulae you should be familiar with (some will be given to you in the exam). Energy transferred = power x time E (Joules) = P (watts) x t (seconds) Energy transferred in kWh = E (kWh) = power P (kW) x x time t (hours) Cost of using electricity = number of kWh x cost per kWh Electrical appliances are machines, they transfer energy from one form to another. For example, a light bulb takes in electrical energy and gives out light and heat; a hair dryer takes in electrical energy and gives out heat, sound, and kinetic energy. Back Waves transfer energy Electromagnetic waves are transverse. Sound waves are longitudinal. Mechanical waves can be either. Waves Transverse Vibrations are perpendicular to the direction of energy transfer Waves can be reflected, refracted (light changing direction), and diffracted (spread out – much greater diffraction when the obstruction or gap is a similar size to the wavelength) 02 May 2017 Longitudinal Vibrations are parallel to the direction of energy transfer. Compressions – where the lines are close together. Rarefaction – where the lines are spread out. angle of incidence = angle of reflection Back Wave speed (m/s) = frequency (Hertz) x wavelength (metres) v = f x λ Electromagnetic Spectrum 02 May 2017 Electromagnetic waves form a continuous spectrum – the EM spectrum Decreasing wavelength, increasing frequency, waves transfer more energy All EM waves travel at the same speed in a vacuum. Some of these EM waves can be used for communications: Radio waves – TV and radio (these can be diffracted by mountains) Microwaves – mobile phones and satellite TV Infrared – remote controls and optical fibres Visible light - photography Back The Big Bang theory states that… Everything in the known Universe was contained at a very hot, very dense initial point. A rapid expansion took place around 13.7 billion years ago in which space, time and all matter were created. There are 2 key pieces of evidence for this theory – CMBR and Red-shift. Big Bang Theory 02 May 2017 Other theories: There are other theories for the origins of the Universe. The Steady State theory suggests that the Universe has always been huge and is expanding because matter is entering the Universe through white holes. However, there is very little evidence for this theory. Cosmic Microwave Background Radiation for Big Bang theory) (evidence If you look into space with your eyes, you will see a lot of emptiness. But if you use microwave detectors you will see a lot of cosmic microwave background radiation (CMBR). The existence of this radiation can only be explained by the Big Bang theory. Red-shift is another piece of evidence that the Universe is expanding because it shows us that galaxies are moving away from each other. Back Red-shift Doppler an object making a sound is moving away from you, the sound waves stretch out wavelength increases, frequency decreases Doppler can also be applied to light, but the object emitting the light needs to be moving very fast and huge distances this is called Red-shift Red-shift is one piece of evidence for the theory that the universe started through a very rapid expansion (the Big Bang) and is continuing to expand (CMBR is another piece of evidence). The faster a star or galaxy is moving away from us, the bigger the red-shift will be. Blue-shift is the opposite to red-shift. If a galaxy is moving towards us the wavelength of light reduces and the spectrum of light is shifted towards the blue part of the spectrum. 02 May 2017 Absorption spectra: These show which colours of light are absorbed by, for example, the atmosphere of a planet or the contents of a galaxy. The absorbed light is shown by dark lines on a colour spectrum. For a galaxy moving away from us, these lines are shifted towards the red end of the spectrum. Back 02 May 2017 Formulae • The formulae you need to use will (probably) be given to you • You should be able to rearrange the formulae when asked If X=YxZ Y=X Z Z=X Y • After that, all you need to do is put in the numbers Back How science works 02 May 2017 • Bias – if research is funded by a company (e.g. a mobile phone company) there is the possibility that the results could be biased, or even not published if they do not favour the sponsoring company. • Reliability – Results are reliable if they are repeatable by others. Results can be compared with others to check reliability. Reliability of data can be improved through collecting lots of data and calculating an average. • Sample size – experiments should use as large a sample of people as possible to get a good representation of a population. How science works 02 May 2017 • Control groups – Used in investigations to allow a comparison to be made. • Issues: Ethical – using people (particularly children) or animals in scientific research Economic – research being funded by companies, governments, etc. Social – how the results of scientific research affect people Environmental – research projects can have a negative impact on an environment even if there is some benefit (e.g. wind farms) Back Interpreting graphs 02 May 2017 • Use numbers from the graph to back up any conclusions • Use terms and units given to you in the graph • Use numbers from the graph as well • If there is more than one plot on the graph, compare the plots in your answer • The graph might show a relationship between X and Y – i.e. directly/indirectly proportional Temperature (oC) Interpreting graphs 02 May 2017 What does this graph tell you? Time (s) • Red starts at a higher temperature than blue. • The temperature of red decreases more rapidly than blue. • Blue maintains a constant temperature for longer. Back Checking your answers 02 May 2017 • After you’ve calculated an answer, have a good look at it and compare it to the question does it look right? • E.g. A student is asked to calculate the mass of some water being heated in a beaker. She gets a result of 2.3 x 1012 kg… • Make sure you use a calculator if you’re not confident doing it by hand! Back